@rbak923 If both are in same risk profile then a family floater policy may work better for you. Only your insurance provider or agent (Policy bazaar /Coverfox etc.) can give you an estimate on premium based on medical history pf your parents.
If possible look for the companies & plans which cover diabetes & stone rather than this being excluded.
When I was searching, I came to know that HDFC ERGO
Optima Restore may not be available for people with Diabetes but ERGO
Health Suraksha might cover them. Please verify and confirm in policy T&C before choosing anything.
Disclaimer : I am neither for nor against any specific company. I only talked & searched about HDFC ERGO and Max Bupa in detail. There may be better alternatives with some other company but you can do that with the steps given in the post.
Caution : Don't break your ongoing insurance
before buying another one. You have already continued the policy for 3Y. Don't let there be a gap in coverage.
Further, if you ask me, I will say that its preferable that there was no opportunity to use Health Insurance for your parents.
And I wish that you keep throwing money in Health Insurance without any opportunity for claim I wish you and your family a healthy future.
I have commented on another post yesterday why all of us need to look at insurance with slightly different perspective. Please check that out.