Couldn't read and not post, although prob not helpful...
Are you going to all the toddler groups you can stand? Sounds like you might need to start 'diluting' your DS a bit, for your own sanity. Are you working or SAHM? If SAHM, can you afford any nursery time? Or a CM would be cheaper, and give DS a better chance to get used to being with other age children.
I'm also thinking that maybe you shouldn't worry so much about the last few days - if your DS was with people he didn't know too well, then yes it would upset his sleeping and make him clingy. He could also be starting a cold or similar, which I found always regressed my DS a good few months in terms of behaviour and emotions.
Do you have a Surestart nearby? They'd be able to give you some advice and possibly help.
And don't listen to your family about the spoiling and miserable thing. Sounds like they're the miserable ones if they can't realise that a child that young - still a baby ffs - needs a bit of extra support in those circumstances, and is way too young to be 'performing' for them.
Is there a DP around? If so, you should also start working out your routine with DS for after the twins get here, to lessen the shock for all of you.
Pecker up girl - you haven't got it easy and I'm sure you're doing a brilliant job