Answer
(Fatwa: 1338/1051=H/1430)
They should not meet in privacy, should not be open and frank, rather they should live with haya and modesty.
(2) It is unlawful. But the male members of a family (father, brothers etc) can eat together while the female members can eat together, or everyone should eat with his wife and children. In short, mixing of brothers in eating with the families of other brother is not permissible. Though father is a mahram for his daughter-in-laws, but mixing and frankness of father with daughter in law breeds many evils nowadays; therefore it should be avoided.
(3) It is lawful provided the Shariah limits are maintained which have been mentioned in under 1 and 2.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband