Your family unit sounds a lot closer than mine. My mum and sister just aren't family orientated.
My sister has never, taken both my kids out together. And she's only had them one at a time, about 6 times over the 13 years I've had DC.
My mum didn't have my first born on his own until he was about 18 months, and only then as her mate had her grandson over, so she wanted to show him off. She claimed she was too old before then (she's the same age as DP's DM, who is keen to have them all the time). If we arrange to see her with the DC, she checks that we're not going to stay too long. (My DC aren't nightmares kids, honest! She just doesn't like having any DC around for too long).
Mu DM and DSIS know I'm going through a rough patch with DP, we are likely splitting up, and they don't call me to check I'm OK, or anything like that. On the rare occasions I've mentioned it to my mum, she's said "I'm sorry there's nothing I can do to help" and that's been the end of the conversation. (Not "what can I do to help?").
I see my mum maybe 10 times a year and my sister about 5 times, perhaps.
When me and the DC are there, they're not really that interested in finding out about my life.
My mum hasn't visited my family home or the town I live in for 9 years. She's too old now, but she wasn't before lockdown. She expects me to come to her unless it was a very special occasion (births deaths marriages, major anniversaries, that kind of thing).
They both say they love me and my DC. They think their way of doing things is perfectly normal.
I try not to let it bother me, but it does hurt how disinterested they are in spending time with me and my DC.
My advice to you is to stop trying to change your DSIS into a person she isn't - she just doesn't see it like you - but be grateful you have a decent relationship with your DM and DSIS. And that they'll actually come to your house if you invite them!
Invite them to come over to see you, and enjoy their company, you're lucky to have them.