1. You can execute and register a Relinquishment Deed duly relinquishing the title of your share of the property in favour of your mother,
2. You can also execute and register a Gift Deed for gifting your share of the said property in favour of your mother,
3. Yes, after acquiring the right, title & interest of your share of the nproperty, she can sell the same to anybody but before that she has to offer it first to her another son who is also having a share in the said property, at the same price she is getting from others, as pre-emption,
4. No. since it is the self acquired property of your grandfather, your son will have no right on it after you have conveyed the title of your share of it to your mother.