Elliso, I have exactly the same concerns, especially having just gone through the baby years and 'come out the other side' and my dc's are now reasonably independent and play together and we do some nice things as a family. I optimistically thought a DC3 would fit in with the family and tag along with the others!
In contrast I am currently lying on the sofa under a blanket feeling rubbish (9 weeks) with Big Barn Farm on repeat on the TV, my poor little DD not being very stimulated. Normally on my days off work we are playdating, toddler groups, out and about, but just tired and can't be ar*ed today! Fear that this will be my girl's existence this time next year.. On the plus side, at least school open and ds back at school today!
dh is now being quite supportive and caring, think he is in denial tho the finances really worry me. have you started looking into cars that four 4 car seats? We will need to trade in our (smallish) car for a bigger old banger.
Told my parents at weekend, and my 'd'dad stormed out and went home! He thinks 'his life is over' as we will call on them to help us out etc. Silly fool! And my dm, who is usually the most optimistic person on the planet, only said 'its going to be tough for you'. Yes, I think I know that.
Felt slightly down that evening, as hadn't been able to be my usual lively person in the snow (a sign of things to come?) and the initial reactions have been so different to my other DC, everyone was over the moon then...
Anyway, better shift from my slothful state, and do something.
Don't get me wrong, I recognise (esp after my Mc) that this is a 'gift' and that at least family christmases will be fun. And there will always someone to visit me in the old persons home when I am ancient, and lots a grandchildren hopefully! Ironically I always wanted twins, just wish they had been dc1 or dc2!
My dh's best friend is a twin. His Dm went back to work 2 weeks after giving birth to stop her going insane. Its always an option I guess...!!!! Ha ha.