Cross marriage and three divorces

I have some questions please guide me

1 what about cross marriage in Islam I mean (one person marry a girl and his brother in law is marring his sister) both of them are brother in law for each other.

2 A person who is working abroad since four years and he did not have any contact to his wife since two years by phone his wife left his house and went to her mother house after only three months later than the departure of his husband to foreign country. Husband tried to call his wife to his home but she refused even parents of

Husband & wife were not interested to solve the problems. Parents of husband were forcing to husband to divorce his wife.

Husband went on vacations to his country but his wife was not agreeing to come to his home. Then husband get married with out informing any body after promising his second wife that he will not bring back to home his first wife.

After passing four years he send divorce his first wife by post three times written divorce in one letter (please not that the day when he wrote divorce he kept with him and think for one weak after he posted it) but also he informed by phone to some of her cousins uncle and his father that he divorced his wife and sent a letter.

Now every body is not accepting this divorce including parents of wife & husband and they return the letter to husband.

And they are insisting to cancel the divorce but husband is still trying to convince his parents that it is not possible in Islam

3 (Is she divorced or not ?) and can husband rajoo again.

I am waiting for your advice.