I probably see my parent 1-2 times a week (through the week or on the weekend) but if we are super busy there are certainly the odd weeks where I won't see them.
My IL's we see 1-2 times a week also, although usually once on the weekend as they work and also live further away. Again though, there may be the odd week where we don't see them at all.
We try to keep if fair but in the end our own family time must come first, it's very important. I think both sets of grandparents understand this.