As far as your uncle's share of property is concerned, it will devolve on Arvind (the so called adopted son),as per the bequest made in the Will, so in that nobody can claim any share as a right.
The property left behind by the father shall devolve on all his legal heirs, i.e., his daughter from first marriage(upon her death to her legal heirs), this children from second marriage, i.e., three sons and two daughters and to his second wife (this will include the share of the deceased first wife), equally, i.e., to be divided into seven equal shares.
The property purchased on the names of three minor children by your father shall remain on the three children alone, nobody other than them has any rights over it.
There is no share for first wife separately, the share of first wife and second wife shall be treated as one unit.
As far as the third question is concerned, you should understand the underlying fact that the third property was bought on three individuals names though your father was appointed as guardian, hence upon becoming major all the three sons have equal rights i.,e., 1/3rd each despite the fact that the son Arvind was adopted by the uncle or not.