Is it permissible for me to name my first son “Kassim” ?
The Prophet (PBUH) prohibited combining his name and his nickname, but using one of them is desirable.
Is the marriage contract considered valid if concluded at home by the marriage official (Ma`zon)?
Yes, it is valid as long as it is registered at the court.
My father passed away before my grandfather. Am I entitled to any share of my grandfather`s inheritance?
All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
According to Islamic courts, you are entitled to what is called obligatory bequest (The distribution of estate to grandchildren who has either lost a parent before the death of the grandparents). Therefore, if your grandfather left such bequest for you, then take that share or else it is more prudent to take nothing. And Allah The Almighty Knows Best.
Does touching women temporarily forbidden in marriage nullify ablution?
It is prohibited to touch, or to shake hands with such women as they are considered strangers, and doing so nullifies ablution.