My husband has 2 kids in their twenties. A daughter (will call her N to make things easier) 22, and a son 26 (will call him T). T and his fiancé have a 3 year old and a 5 year old together.
N, T and T's fiancé are all very close. They don't live together but might as well do as they spend each day at each other's houses. Me and my husband are a few miles away. My kids are similar ages to T's kids, 4 and 2. We feel repeatedly cut off by them. My husband suspects N and T resent my kids because they grow up in a stable environment, whereas my husband divorced their mum (who cheated on my husband). I could understand that but even after the divorce, my husband was always heavily involved in their lives even after he met me.
The issue is that I feel my kids receive no affection from their older half sister. T doesn't bother with them either but I understand that as he has his own kids to think about. For example, I invited them all to a soft play centre for my daughters 2nd birthday, and none of them turned up on the day. I eventually managed to contact them (they were all going together as they live so close to each other) and they said T's 5 year old saw a Nando's on the way there and wanted to go there instead, so they did.
N completely spoils T's children. I understand they are her nephew and niece, but my 2 little girls receive nothing from her or T. No birthday presents or even a card. But T's children are given absolutely everything. N spends over 200 in presents for each of them on their birthday. They're off to Applejack's tomorrow, as always me, my husband and kids aren't invited. I don't expect them to invite my kids to everything for free, nothing of the sort, but I wish they'd at least ask us to accompany them along to things occasionally for the children's sake as they are similar ages. Of course T and his fiancé have no problem wanting us to babysit when they go out.
Me and my husband's parents are both dead, and neither of us have any siblings so it's not like my kids have any other family to bother with them. Whereas T's kids have me and my husband, N, and their mum's side of the family.