I was thinking the same Redhead.
7 years is long time Sallywally, it's 9 years for us and FWIW I think you've done the right thing, hard as it is. In your position I would continue send cards to the GC but no gifts, and nothing more to your D.
We've never sent gifts to our GC but always a card for their birthdays and at Christmas but nothing at all to our ES. We stopped this year but not because cards were ever returned, they were most likely binned, or because we were told to stop, it was something we no longer felt we needed to do.
We've never known our GC but I understand if you did, and they knew you, you would never want to stop just in case something got through to them.
As for your s.i.l, sod him. They're your GC whether he likes it or not. We're as certain as we can be that our estrangement is due to our ES's wife being manipulative and using coercive control.
If she had sent me a nasty text telling me not to send our GC anything, she'd have been left in no doubt how I felt about that.
If you haven't done so already, think about a memory box for your GC where you can put their cards and also consider a savings account where you can put something in for birthdays and Christmas.
You can open them in your name and if heaven forbid you never get to see them again, you can leave the account details in your will, together with itemising the memory box, in the knowledge that there will be something for them to inherit which shows them you never stopped loving them or forgot about them .