Not that I think you're unreasonable in your opinions, but this threads has gone on so long that actually it has become unreasonable. I know you didn't like your in-laws mentioning your mum negatively, how would your DH feel reading this? It makes me feel uncomfortable to think that, what has become our entertainment, has stirred things up out of all proportion.
I hadn't heard of CMV until this thread and I've had two children. It was in no literature and not on the midwives' list of things to warn me about... is there the smallest chance that your SIL didn't realise the potential danger?
I can't even really see your PILs as 'evil' their original crime was to assume they'd be welcome at yours and didn't think through your impending baby and housemove very well... sometimes you need to point out the bleeding obvious, it doesn't make them evil.
Sounds like the whole family has it's fair share of crazy times ahead in May-July, and I think there's always room for understanding, and compromise.
How it reads to me, as someone who only read this thread last night, is a few incidents where someone(s) have been unreasonable and your DH being a bit slow in understanding your stress at the thought of it all, and perhaps, you not saying right at the beginning "This is not going to happen".
I don't understand how it's got to the stage of calling them evil/horrible/selfish/twats. I don't understand the frenzy. I don't think YWBU but I think you are now to let this continue, just as you are your DH's priority, he should be yours, and you've allowed people to rip his family apart on a public forum, where you WILL be easily identifyable to anyone who knows you because of the details of your lives you've given. I would ask for it to be removed if I were you, for your DH's sake.
Do what you're comfortable doing, nothing more. Good luck with the new baby and house move, I don't think you're a bad person at all, and agree with much of what has been said, but I think if any of your in-laws saw this they would be justifiable upset and angry, because they have no right of reply. x