First off, congratulations on your multiple pregnancy (I take it you're projecting that the twins will be 3 mo at the time of the trip?). Being in a family with multiples is an interesting, challenging experience - we wouldn't trade it for the world!
But...
Personally, we found being out and about with newborns (eg 3 mo old and younger) a bit challenging, but that was probalby due partly to our weather. I personally believe (and personally experienced) that breastfeeding infants is easier than lugging bottles, nipples, bottle liners (if you use 'em), and formula or expressed breastmilk around....so that actually makes things easier.
What might make things harder is not knowing the health of your two little ones (what if they arrive early? what if one or both have lingering health issues?) nor how you and your partner/husband deal with the two little ones. You might not have much time between all the requisite baby activities for both babies to do much else -- looking back at our log for that time, I can say with confidence that most of what we did was: single or tandem(double) nursing, changing diapers and putting the girls down for naps/bed. We had very little time during the day for anything other than these activities....simply because you've got two separate little people to care for.
The upside of your trip would be having help around *and* not having to cook or clean or do laundry. The downside could be that you and your partner/husband don't have enough time to *do* much other than take care of your twins....I would suspect that you would still be dealing with some of your own baby-induced sleep deprivation, which would make enjoying WDW more of a challenge...(based on our and our friends' experiences in the twins' club).
Basically I think if you set out to do it, it would be an adventure!

A fun one but challenging and potentially difficult...depending on a lot of factors you wouldn't be able to predict at your 45 day deadline for payment :-( If you live close by and are Disney vets, you might do fine. If you have to travel a long way and this is more of a 'trip of a lifetime', then I'd probably suggest against it (or going in with VERY low expectations).
Personally if I *had* to recommend something, I'd suggest putting the trip plans aside for a while, and going when they are bigger and easier to manage (12-24 mos), but that's just me. I'm sure it's doable but just not easily slotted into my experience with 3mo twins.