My in-laws also say we are too strict and we need to “let them be kids”. But at the end of the day they are YOUR children! That’s why they are the grandparents, they can let them get away with that but they need a stable foundation and a loving home. If they have that then what’s the issue. Don’t feel bad that they don’t agree with you, children need to have boundaries and rules in life.
Good job mom and dad. 
Awesome work I feel yah