1. if mother's share in property defined as 50% then yes sales consideration for her is Rs. 45 Lakhs , amount paid to uncle is considered as out of sales consideration thus use of such amount by uncle is no matter.
2. yes you can open capital gain saving scheme account and part amount for purchase property in next 2 years and save tax but if you not purchase property then the amount will become taxable.
3. prepare your mind to buy or not property today and then deffer the event but decided later is not advisable.