The only type of laws that may sometimes be overridden to help with shalom bayit (promoting peaceful family relations) or kibud av va'eim (honoring parents) is rabbinic law, not Torah law. A rabbi should be consulted in these cases.

Ba'alei teshuva often have problems with issues of kashrut in their parents' homes. Pots, dishes, and utensils might not be kosher or toveled. Consult a rabbi. Questions of bishul akum (cooking that was done by a non-Jew) might apply to non-shomer Shabbat parents, but the custom is to be lenient.

If the parent's kitchen is known to be non-kosher, food must be prepared with care (see How To Use a Non-Kosher Kitchen). If the parents do not lie to their children, they may be trusted as to the source of food and its kosher status.

Since we may not eat from dishes or utensils that have not been toveled (immersed in a mikva), you may  want to consider toveling your parents' dishes or utensils, or using disposable goods. In such cases, it is OK to use china that has not been toveled.

Shalom bayit is a family at peace, as one unit. When leniencies in law are used to avoid intrafamily conflicts, customs and d'rabanan halachot can sometimes be overridden. But d'oraita halachot may not be violated. Consult a rabbi.
Situation
You want to go to minyan but your wife is overwhelmed with trying to feed several children and she asks you to help.
What To Do
You must miss minyan and help her since your wife's needs take precedence over your wish to pray with a minyan.
Note With shalom bayit problems between spouses, a rabbi should be consulted for details.
Note Once someone is married, his or her in-laws are part of his or her family and are included in shalom bayit rules.

1. Place arm tefila box (bayit) on center of bicep of whichever arm you do not write with (knot on the arm tefila should touch the side of the box). If you are ambidextrous, put the tefila on your left arm.
2. Say the first blessing, “lehaniach tefilin.”
3. Tighten the strap.
4. Wrap the strap around your arm seven times between your cubit (inside of your arm, opposite the elbow) and your wrist.
   Note If you wrap more times, it is OK.
   Note You may wrap the tefilin strap over a wristwatch or put a watch on top of the tefilin strap.
   Note Tefilin straps should not overlap with each other and should not be wrapped on top of the ulna protuberance, but if they do--it is permitted.
5. Wrap the excess around the palm of your hand (tuck in the end to keep it tight and out of the way).

Say bracha meruba ba'bayit ha'zeh only when eating in a house or apartment that is occupied by a Jewish family or a Jewish owned public building.

Say ba'alat ha'bayit ha'zeh if the head of the household is a woman.

An onen ends shiv'a (and shloshim) with the household head ("gadol ha'bayit"--whoever controls the money in that household)—even if the household head begins shiv'a before burial and the onen joins the shiv'a house after burial.

The original purpose for lighting Shabbat candles was to enhance the peace of the home (shalom bayit --so that people could walk around without stumbling in the dark), and so Shabbat candles were lit where people would eat dinner Friday night.  But we now rely on the idea that candles help provide a festive atmosphere.
 

Praying with a minyan is very important and you should travel up to 18 minutes away in order to get to a minyan.

“Be holy because I, the Lord your God, am holy.” Leviticus/Vayikra 19:2
 
Halacha ("The Way To Go" or "Way to Walk") guides proper Jewish behavior in all aspects of life, each day of our lives--not just in civil laws or court situations. Halacha teaches us how to behave with our families, relatives, and strangers as well as how to fulfill our religious requirements between ourselves and God.

To fulfill our role as a holy people, we imitate God's actions. Examples are visiting the sick, welcoming guests, giving charity, refraining from creative activity on Shabbat, and promoting peace between husband and wife (shalom bayit).

The true reason for following halacha is because God commanded us to do so.  We observe halacha to please our Creator and to become spiritually close to Him by doing His will and imitating His actions.

Like the word for the whole body of Jewish "laws," each rule of how to act is called a halacha (plural, halachot).

Where Do Halachot Come From?

Although you will find halachot on this site that were born only a few days or a few decades ago, the body of halacha has been around since before creation.  "God looked into the Torah and created the world," says the Zohar, and so we find the Patriarchs followed halacha even before that great law book, the Torah, was given on Mount Sinai four centuries later.
 
Many halachot are specified in the Written Torah (Jewish Bible). These halachot correspond to fuller and more detailed halachot given orally (Oral Torah) to Moses on Mount Sinai to explain the Written Torah that he received at the same time. Many halachot could not be understood from the Written Torah without the Oral Law (for example, what should be written on a mezuza scroll?) and many common practices such as making kiddush or what tefilin should look like are to be found nowhere in the Written Torah.
 
Since the Torah applies to all generations, the Torah specifies that there be wise and learned people to decide how to apply halacha to the situations of the day.  Halachot can be found in sourcebooks such as the Mishna, Gemara, their commentaries, Shulchan Aruch, Mishna Berura, and responsa (questions and answers originally sent by letter and now, occasionally, by email or SMS!) of later rabbis.
 
Sometimes a custom becomes a halacha, sometimes not.  For example, the original halacha for tzitzit was that a Jewish man who wears a four-cornered garment must have tzitziyot on each corner.  The custom, which has become universally accepted and now has the force of halacha, is that Jewish men wear a four-cornered garment in order to be able to fulfill the commandment of wearing tzitziyot.  An example of a custom that did not become a halacha is that some men and boys wear their tzitziyot outside of their shirts and pants.

Levels of Halachot

In halacha, there are three levels of what to follow or observe. They are differentiated on this website by the following terms: 

• “Must”:  Halachot that are generally non-negotiable except in extreme situations;
• “Should”:  Customs that have been accepted by the entire Jewish world (or major segments of it) and that may be overridden when necessary, sometimes even if not extreme circumstances; and
• “Non-Binding Custom”:  Customs that are not universally followed and that do not need to be followed except by people who have the tradition to do so.

K'zayit is variously defined as being the volume of 1/3, ½, or 1 whole egg; 0.6 - 1.9 fl. oz. (18-56 ml), depending on the application.

• K'zayit for Seder Matza and Afikoman:  1.9 fl. oz. (56 ml) of matza.
• K'zayit for Bracha Achrona and Birkat HaMazon: 1.3 fl. oz. (39 ml, or 1/6 cup) of solid food.

Beitza, K'Beitza = 1.9 fl. oz. (56 ml); an egg size by definition.

Although the mitzva d'oraita is to thank God only when you are satiated from the meal, chazal decreed that we say birkat ha'mazon even when eating only the volume of a k'zayit and even if not satiated. So you must still say birkat ha'mazon after eating at least 1.3 fl. oz. (39 ml, or 1/6 cup) of bread within four minutes--even if you are not full.  This is known as birkat ha'mazon d'rabanan.

To eat more than one type of the Five Special Fruits:

• If you have a particular preference, you may eat the fruits in whichever order you prefer.
• If you have no particular preference, eat them in this order:
  1. Olive
  2. Date
  3. Grape
  4. Fig
  5. Pomegranate.