Hindu law

legal heirs of a are his mother (alive),wife (dead) and children

legal heirs of b are her husband (dead) and children.yes a and b  require seperate lhc

Ans. In this case the legal heirs of A (husband) are his mother, his dead wife B and his only son consider X. His dead wife's share will go to his son X.

Now legal heirs of B (wife) are her dead husband A and her son X, In this case the dead husbands share will go to the child X.

So here 2 separate Legal heir certificates are required each on for A and B.

Further in liquid assets, it may also depend on who is the nominee on papers like FDs, shares and the like. So an order to this effect, where the legal heirs can claim accordingly is also needed.

You have not mentioned your religion.  By your name assuming that you are hindu, the following procedure is that:

If the male hindu dies intestate the property will go to a) sons b) daughters c) wife d) mother.

If the female hindu dies intestate, the property will go to a) sons b) daughters c) wife.

As per the above point, you can extract the answer you want.

Yes. I am guessing the above rules is same even if the only son is minor.