Property rights of son

If your mother dies without executing a Will, her property devolves among you, your siblings, and your father if he is alive.  Now she can perform a gift deed in anyone's favour as she is the owner of the property.  Your son has a right over your share.

Since your mother is registered and absolute owner of properties so either she can or through registered power of attorney holder sell the properties to anyone .your wife and son have no right to make objections but in case your mother dies intestate then you and your siblings and  your father( if alives ) have equal rights and share in properties of your mother but your son will have no right and share in your mother's properties. 

Your mother's property is her own hence if she dies intestate then it will devolve equally on her own class I legal heirs which are you and your female sibling .

The share of property inherited by you becomes your own and absolute property which cannot devolve on your son or your wife at least not during your lifetime, hence your wife cannot claim any share on behalf of your son as a right in that situation.

The properties are stated to be owned by your mother and not transferred in your name hence you have no right, interest, claim or title to dispose it off.

Even after death of your mother your sister has a right in the intestate property left behind by your mother.

However, your son and wife do not have any share if your mother did not make any document for transfer of properties in their name(s).  

Without will, this property will be considered as Inherited or Self-acquired for us ( me & sister)??

It will be considered as "inherited" if no other LR of your father is there.

You, your sister and father, if alive,  are legal heirs of your mother. Your children and your sister's children will have no rights so long as you and your sister are alive. You can sell your share of the property, provided the property has been partitioned. Your spouse also may have right over your property after your death unless she is divorced.