what should you do if you encounter your old and stubborn parents?

what should you do if you encounter your old and stubborn parents?
My parents are over 80,they are stubborn and critical.
More often they make mistakes,we point out,they never
accept and retort that it's our fault.They are muddle-
headed,even they don't common sense and never listen
to our critical comments.They just do what they like
no matter they are wrong or not.Sometime we ignore
their mistakes,and pretend to agree with them 100 percent
on the surface,but 100 percent disagree in the heart.
I never dare to discuss heavy topic with them,I just
talk about light subject and become a yesman.A little
thing will trigger their anger and misunderstanding,
I just really get tired of them.A little thing will
be taught many times until they understand.What should
I do?