is this sentence is correct - Ritu and Sumit’s house is very beautiful .
Yes, this sentence is correct. But if it was; the performance of Ritu and Sumit was liked by all then it would be;
Ritu's and Sumit's performance was liked by all. This is because we are talking of individual performances which is clearly explained in lesson 4, I guess!
good luck for more improvement to you(arulshrestha), Nikita0831 and for all.