1. yes can be done
2. but dont write in agreement that transaction will be completed within 3 years
3. you can write that transaction shall be completed within 1 year from date of signing and the same is mutually extendable by the parties subject to the extension not exceeding a period of 3 years from date of signing
4. the deposit which you will get now can be shown as an advance for sale of property. Then it wont be taxable because if the agreement does not go through, you will have to refund that deposit to buyer. However any interest that accrues on such deposit will be taxed as income from other sources
5. you can make a MOU and have it notorised
6. reason for point no.3 - if you write 3 years, then you are essentially locking your property for 3 years and wont be able to sell to any other person for 3 years. However if you write as advised in point no.3, then if on expiry of 1 year from date of signing, you find a new buyer who is willing to pay you higher than what your relative has offered, then the agreement can always be terminated and you can refuse to extend the time limit beyond 1 year. Further the relative cannot force for an extension because it will be written in agreement - that any extension beyond 1 year shall be on 'mutual' agreement between the parties. You also need to factor in this - if you lock your property for 3 years then you are also foregoing any increase in price of your property that may happen in next 3 years