Yes they can have yiour share. If it’s fathers property then all legal heirs will have equal share

It is necessary to peruse the document signed by you 

during parents lifetime you don’t have any share in their property 

on their demise intestate you will be one of the legal heirs 

your children have no share in maternal grand parents property 

Before actual inheritance deed of relinquishment is not enough.

In other words on death of your parents you will be entitled to inherit their property unless they leave a Will or during their  lifetime they execute a deed of conveyance.

Marriage is a bind between two families  and they must be done with blessing of respective parents. 

You have already relinquished your right before registrar office so now you cannot claim. secondly as per law you being son donot possess any right in the properties of parents. It is mercy and sweet WILL of parents if they give you any share in their property but legally as a matter of right you otherwise cannot claim.   

Legal heirs of a convert to other religion are not entitled to share in the  ancestral property but the  convert, in this case you, cannot be denied share in the  property in spite of the  declaration  made by you in the  office of Sub-Registrar. The  reason is said declaration  is made under duress and coercion and not willingly. You can get the  said document as not binding on you from Court and claim your share in the  property. File a suit for declaration .

Maternal grandparents are not ancestors neither the property left behind by them are ancestral property.

Moreover you have already relinquished your rights by a registered deed hence any claim made by you during your mother's lifetime may not be maintainable.

As you have signed a deed of relinquishment releasing your proportionate share in the property, you cannot lay any claim over it now. Your children's inheritance shall be only through you. Since you have relinquished your share legally, they are not entitled to any claim.

- If you have given a registered release deed or an undertaking that you will have no right over the property , then you cannot claim any share in the property of the parents. 

- However, you should peruse that document that whether this documents have been given even on behalf of the children's or not. 

- Further, your daughters have no right to claim over the property of your parents during their life time. 

Generally, if you voluntarily signed a document at the sub registrar office relinquishing your rights to your maternal grandparents' property in exchange for a sum of money—even if you never actually received the payment—that waiver is typically binding. This means that your legal claim, and by extension any claim your children might have inherited from you, is waived.

However, if you can prove that you were coerced or unduly influenced into signing the document, or that it was executed fraudulently or without proper consideration, you might have grounds to challenge it in court.