I completely agree Eustace - and if I thought they were better supported over there with homework etc. I would see their point a little bit more - however we feel that they're using the two asd siblings as an excuse - since they've been over there primarily, they've dropped all extra-curricular activities, and DS has started having issues with not having any friends. From past experience, the attitude towards education in XP's very large family is that you do the minimum amount of school work and that should be sufficient, as it's more important to have fun outside of school hours. Over the years, DH and I have encouraged and supported them to do things outside of school - maybe one or two activities, so it's not like I've pushed them to do loads of things. I've even tried to teach them something in my specialty, which they've enjoyed and been really good at, but then when they go to XP's, it's discouraged, forgotten, and lost, until they end up giving up.
I'm doing a degree in DC1's A-level subject, so am happy to help them both with that subject, and other subjects that I've specialised in in the past, as is DH. All of DC1's commended homeworks were projects that DH or I helped with.
Contrarily, in the last year, DC2 has missed homeworks, and his reports haven't been as good as they are normally. Although, when his last report arrived, and there was a grade that seemed concerning, DH and I raised this to be told that actually it was completely fine and all to do with the curriculum and grading changes. We said ok, as there was not a lot else we could say, but now XP is saying that I always put DC2 down and don't acknowledge his achievements.
I think a lot of it stems from the fact that DH and I have had a stable household here for a long time, whereas XP has been living at his parents house for about 9 years. It's also probably not coincidental that he's done this two weeks after moving into a house with a new girlfriend, who the DCs only met a few months ago. I have no idea what this lady is like - I'm sure she must be fine, as from what little we've been told, she's a nurse in a care home, but the DCs don't seem too louch with my mum, so that's something, but it's just really strange how one minute she'll say she'll come round, and then she ignores my texts. I'm trying not to text too much for fear of that being seen as harassment, and haven't rung at all. But other than sending the odd text to offer to meet up, I don't see that there's a huge amount I can do but wait to see if they'll come to mediation.