Hi there - this is definitely a tough situation, and I also know how hard it can be to set boundaries with your parents.

There's an article on this site called:
Tips on Setting Boundaries in Enmeshed Relationships

That has some good tips.

It sounds like they need positive reinforcement and it couldn't hurt to take a breather. Maybe even let them know how much you love and appreciate them, enjoy spending time with them but also need to have your own time and remind them you will be there to visit them the next time around.