I think if you've only invited dc over twice in all that's not much to go by. If you like the dc you had over, invite them again, or try inviting other dc, if you're happy to do that. I imagine at some time it all just takes off with invites back and forth.
I don't do playdates if I can avoid it but dd goes if she is invited. I don't generally invite anyone back although I have sometimes done it in the past. Dd's best friend is a wild (but likeable boy) but I can't face having him round. He's too much for me but not a bad kid in any way. His dp love having dd round though because of course they're used to their ds's wild ideas and dd has a sort of calming effect on him so it makes him easier to handle IYSWIM whereas having him here means bedlam and I'm not used to it.
Dd was invited to a little girl's house on Friday and she looked really upset when I came to pick her up. She found the girl too bossy and said she'll never go there again and won't have her here. In a case like that it is tricky. I can't repeat that to the dm without offending her but I would find it weird to invite the girl round against dd's wishes - and dd is VERY easy going (unlike me). So unless the dm expressly asks me whether her dd could come and visit, I wouldn't invite her.
On Tuesday we were invited to a boy's place who dd doesn't like much but I didn't like to refuse. It was ok but I noticed (I was there the whole time) why he gets on dd's nerves and she did say she didn't want him to come here. Frankly, I'm not keen either so I'm hoping to get out of inviting them back.
I've had little girls over in the past who were very difficult to please and even really catty despite being maybe 4 at the time. Dd isn't like that at all and I found it a real turn-off TBH. I don't think I am a great lover of children TBH. Some I like, some I don't but there aren't many I like having in my home.
I can imagine what probably happened in your case is that the mum just asked "who would you like to invite over?" and the ds answered "the twins" because he'd been playing with them that particular day. I don't think you or your ds are being snubbed from what you've written.