My Mum's partner is awesome. I think she was in her early 50s when they met, he was in his late 60s. So his kids are much older than us (one of them just turned 50). We've met them once or twice but have nothing to do with them (not for a bad reason). My Dad died when I was 19, so Mum's DP is Grandpa. I asked him if it was ok (the kids wont have another Grandpa on my side), and he was honoured. In saying that, if they split up (they wont, they're awesome together), I think he'd drift away and probably wouldn't have much to do with him, not because we don't love him, just because it's not a blood connection.

My Mum's ex-DH (married around the time Dad died - they'd been split since I was a kid) had two kids closer to our age, one I was quite good friends with (went to the same school), but they weren't our brother and sister. I only have two brothers and we have the same parents.

Weird isn't it. Guess it would be different if they'd been together since we were little or if we'd lived together.