1. You can do nothing with regards to the properties which are exclusively owned by him. However in those properties wherein your mother was a joint owner, you have share in it.
2. To claim share so the properties may not go waste , you can file a suit for partition wherein you seek injunction as well to ensure that those are not sold in the meantime to frustrate your claim.
3. if you have no proof on payment of Rs.20 lakh I do not think you can recover those.
4. Your father is a matured person and must be well aware of the consequences of the acts done by him. You better leave him alone.