Is the wife obligated to serve her husband's mother, father, and sister who live in their home, or is she only required to serve her husband, especially since the husband's mother serves her daughter who lives in the home?

A wife is not obligated, شرعًا (by Islamic law), to serve her husband's parents. Her service to them is an act of favor on her part. If she does not serve them, that is justice.

It is not permissible for the husband to force his wife to serve them, and the mother does not have the right to be displeased if the wife does not serve her.

The husband must exercise wisdom by not displeasing his mother nor wronging his wife.

The belief that the entry of a woman who has recently miscarried into the presence of the mother is the cause of her relapse is a false and baseless superstition.

Supplication (Du'a) and seeking forgiveness (Istighfar) are among the greatest means to conception.