Sink is alright. I am not sure but sometimes I get that sound if the paneer has been made with too much of the curdling agent. You should add it little by little and stop as soon as the water begins to clear. See if it helps.

No you do not have to grind it any time. Just soak rice and curd as it is.

Thanks Meenakshi. Hard can be if over baked or your raising agent is not right.
I don't know what you man by jars. Do you mean muffins? cup cakes as they are called too. I have not seen jars as such. Do clarify, any cake shop would have muffin moulds or cups..

In any recipe which has butter or oil substitute with same amount of cream.

I have no idea of the paneer in the US. The important thing in rasgulla making is that the paneer should be made of cow's milk, and the less rich in fat the better.