curtains you have to do the best for your family. Lots of posters here say your visits are too low, but they are basing it on their own relationships with their parents.
If your parents expect to be waited on, then either they become more hands on and thus see dgcs more often, or they just have to accept that the dgcs have their own lives and see them less often. Personally, I don't see a problem with once or twice a month.
I see my mum about once a week , on a weekend, with DCs, BUT she lives 10mins from me and we all get on( no problems with me or DH). We can't see her during the week because the DCs, like yours, have after school activities plus need time at home for homework. My DM doesn't mind- she knows she'll see then at the weekend- and certainly doesn't moan about it.
DM knows that we all have our own lives to lead and is happy for the time she does have with DCs. If she wants to see them more, she'll ask if she can come round, which is always welcome( except after school activity night where DCs finish at 5pm)
They are still young 5&4, so dinner time is 5.30, bath at 6.20 and bed for 7pm.
My Pils on the other hand, live about 2 hours away so see DCs about once every 4-6 weeks, at the weekend, when we stay overnight. Of course they would like to see the kids more but again, they don't moan about it. They know that we have lives to lead too and they are happy for the time they have.
Both sets of gps are very reasonable. They know its not fair to put pressure on us to see dgcs, and if they wanted to see them more, they would visit us.
I think it's unfair to be moody with you because they don't see dgcs as much as they would like.
Do you feel you should see your DP more? If you think that what you're currently doing is fine, then you explain again the reasons-laying out the DCs timetables if you have to.
You have to do what fits you and your family and not made to feel bad because your mum pulls a mood.
Hope you find the best solution.