OP, I'm not sure about their 'obligations'. As a full-time working parent, I don't really have spare time. My outside of work life consists of....
evenings - helping with homework, cooking supper, tidying kitchen, getting me & ds sorted for next day etc.
Saturday - laundry, 1 hr exercise, ds to swimming lesson, food shop, lunch, then chores like cutting lawn, washing car, hair cuts etc. Possibly have a friend drop in for half an hour for a coffee.
Sunday - house work, life admin, batch cooking for the next week, spending some fun time with my child myself - maybe a cycle ride or cinema, then take ds to his karate class.
I would struggle finding time for a regular 2-3 hour visit as well. And do your dgcs want to come? How old are they? The last 6 weeks have been summer holidays. Are your dgcs at holiday camp? Out with their friends? My ds disappears on his bike after breakfast and only reappears for food.
Can you not meet them in town, or go and watch them playing sport? Build your time into the dgcs schedule.