If the husband is the disciple of a Guru, does the wife automatically become the disciple of the Guru?

Yes, if the wife wishes so.

Is marriage between sub-sects of a caste permissible?

According to me, it is okay.

For a person in family life, be it male or female, is it necessary to adjust with their spouse in daily affairs even though s/he is wrong, or can s/he take to righteous path? In what way is a spouse important for a person for the order of worship is Mata,Pita Guru, Deivam?spouse

In order to carry out any activity – spiritual or otherwise, peace is a must. Only if there is a mutual understanding and adjustment will peace prevail in the family. Hence it is important.

Often we see that there is no compatibility between the husband and wife in a family. Why is it so? How can a marriage be made successful?

In any relationship, you give, before you expect others to give you. Similarly, when it comes to love, you show your love before you expect to be loved.
As long as marriage is considered as a divine bonding, it is blissful and the life is charming. As soon as we think that of marriage as a mere social binding governed by law, it loses it charm and becomes dry and listless.
The best way to ensure that the marriage continues to be a divine bonding for ever, is to pray to the Supreme Lord, Sri Krishna. He is an embodiment of divine love and nothing but pure love and love alone. He will shape your life in a way that would bring mutual understanding and love in your family life.
The easiest way to pray to him is to chant the Maha Mantra. Continue to chant the Maha Mantra with unflinching faith and devotion.

When will my husband start loving me?

Your husband will start loving you when you love him without expecting his love.