Deceased husband property was jointly with husband father and brother ----- When did they purchase the property ? Whether anchestor property? If they purchsed property jointly whether it was shown as HUF or individual
Property purchased by father ---- It will be taken as property self earned but for dispute sake HUF can be taken , whether maintainable or not depends upon in dept analysis of documents
Custody rights of minor children --- Will be with mother as per Hindu Minors and Gaurdianship act . Whether she marry or don't . But if some one is able to prove in court that children are not taken care of properly then looking at circumstances court can pass orders only from view point of children no one else
Father in law can wants to take care of one child --- Yes he ca do it but it has to be then put properly withing frame work of law with help of local lawyer , Oral words will be risky in future.
Hindu Minors and gaurdianship act --- This act have provision under circumstances that brother who is CA and wife M Com wants to give better life. In that circumstances proper appliation have to be brought in front of court under Hindu Minor and gaurdianship act. additionally it will be better that sister also comprmise and take decission in welfare of children. But if you go for adoption then the child will loose right of his natural parents property etc. So you should understand difference between Adoption and gaurdianship \
5. No father in law can not deny all rights if widow marry, similar provision is made in 2005 amendment of act. but at same time father has right to make will , if maharsahtra then he can transfer his assets (Sell) to some one and bypass her right. So at time claiming that it is HUF will be ok , but once you take dispute it will lead to only legal fights and bitter relationship
6. Mother of child can file for gaurdianship so before things get settled better steps under Hindu minors and gaudianship act is taken. Additionally remember by this act if child care is not taken properly the even from natural gaurdian , court can take child and give custody to some one else (Like when father is alcoholic , drug addicit etc)
7. See anyone can file suit for gaudianship of minor claiming child is not been taken care properly , How they prove it and what circustances they prove it depents. So it will be too early to comment on it
8. Remedies for it will be CA brother and wife take gaurdianship from court with concent of their sister and take care . Adopting children will be permanent solution but then children will loose all their rights in their fathers property etc. They will have only right in your property no one else