My question is how i can challenge the will ? As per Shia Islamic law a father cannot give more than 1/3 or 3/4 property without consulting other Son's , As he says whole ground floor is his it means whole land belong to him what about others?
You can challenge a Will only when he is forcibly acting upon it. You can file a partition suit seeking your legitimate share in the property. Let him come to the court with his so called will, then the will may be challenged. You are right that as per Muslim personal law a person cannot bequeath his property beyond the extent of 1/3rd to anyone.
CASE 2: if we go for case 2 when my grand mother was alive she said this property is given to me in meher (verbally) filled a form of municipal corporation and transferred the name from my grand father to grand mother now the tax is paid in the name of grand mother but registry is still in the name of grand father.
If she claims that the property was given to her in Meher by her deceased spouse, it can be construed as valid statement because the same was acted upon by her by taking possession and changing the records in the Municipality. This is an established proof that the property now belongs to her. She can very well file a declaratory suit to declare her title in the property based on the documentary evidences in her possession.
On which way we can challenge and get our part? (As per Muslim Shia Law)
Filing a partition suit will be an option before you. Filing a declaratory suit by your grandmother will be another option before you.