So his new work colleagues know that he has a wife with disabilities and a small daughter with special needs, but for the first 'social' meeting they're going to be introduced to a 'gorgeous, single' plus-one instead, with the explanation that sadly his wife couldn't make it as she has to look after their daughter?
He does realise that that's going to make him look a bit of a cock to them too, yes?
OP I get exactly where you're coming from on this - I too would not like it one little bit. Pull every element apart and you can argue the toss, it's not black and white - but as one big picture it is Not Ok. Yes maybe you should be going, maybe he's right to feel aggrieved or simply resigned to the fact that you won't come (thus explaining the asking your friend first, it's not necessarily dodgy). It does sound as if you need to do a lot of talking and face up to some issues that are only going to get bigger and worse over time. It's not necessarily one person's fault more than anothers, not at all.
But the fact remains that this doesn't look good - it's not a good first impression to make to these new colleagues, for either of you. At best, it makes you look sidelined. At worst, a few of the group will be having conversations on the way home along the lines of:
- 'Well I wonder what's going on there then!'
- 'She's his wife's best friend - apparently'
- 'His wife has a disability and his daughter has autism, maybe they genuinely didn't want to come.'
- 'Do you reckon he's ashamed of her/them? That's awful if so'
- 'Maybe it's more that she's not the type to socialise, maybe it's difficult for her'
- 'Yes but still, bringing another woman to meet your new colleagues before they've even met your wife? Must be really difficult for her if she's the one who's disabled and the one left caring for her daughter...pretty selfish of him...'
Etc. etc.
Honestly, it's a situation that makes you a possible topic of gossip and, to be frank, will almost certainly make several of the group raise their eyebrows at him. He should think this one through a lot more carefully, I'm afraid, even if just for his own sake!