OP, they, and you, have recently had to change childcare arrangements, so this is the 'getting into a new routine' phase, which takes a bit of time.
I think that with the new set up, you've obviously got a lot more free time to ruminate and overthink things at the moment, while the exact opposite is true for your DS and DIL ?
I think that it might be nice to change your angle of thought a bit ?
OK, so you can't 'pop in to see DGS at any time' and your DS and DIL are probably not yet settled into the new routine enough to be thinking about facilitating a new 'visiting routine', but what about trying something new for a while ?
Perhaps you could take the kids to some of their after school activities ?
If that wouldn't be too much physical activity for you to pick them up then watch them at their activity ?
Perhaps you could buy an ipad so you can have face time with the kids ? Maybe help with homework or play a boardgame ? That way you're occupying the kids and spending quality time with them, but not disrupting the whole 'home routine' ?
I'm sure you could think of other options/ideas, that you could physically manage , that aren't too much physically for you ?
You're going to need to be proactive in this, because the 'duty' visits to GP's, Uncles/Aunts/cousins etc really doesn't exist now ? But you're an articulate, intelligent woman, and if you can find something that works for you and them, all your lives will benefit ?
Please don't be 'that' GP, who sits and moans constantly about being ignored/left out etc, and bemoans the modern lack of 'duty' etc, but who does sod all to change the dynamic themselves ?