1) As living in the Indian joint family, if I am performing wuzu and suddenly at the time of masah my brother in law came, then what should I do.

Should I have to repeat the whole wuzu?

2) If I am reading namaz and suddenly non-mahram came and sit behind me and I’m not wearing socks, then my namaz is valid or not? I have to pray it again?

1) You don’t need to repeat it.

2) If you can cover your feet while you are reading Namaz, your Namaz is ok otherwise repeat it