It'll be a real pain lifting them in and out when they are maybe a year old. Easy with a 4 door, but very awkward with a 2 door. And how is a twin seating buggy going to fit in the boot (as well all the other clobber)? As lovely as the GTS is, it really isn't a practical proposition when you have twin babies - it's a car for when they get to maybe about 3 or 4 years old and can get themselves in/out.
If you fancy a Maser, try a late QP V GTS which has the same 4.7 engine, same sound, same chassis, same performance - but more useable space. Ask Dicky Grace to find one for you.
Appreciate the advice, but I am set on the GTS as long as the seats physically fit, which it sounds like they will. The twin buggy we are looking at folds tiny, and the car seats attach to the chassis. The was a type of buggy which easily fitted in the boot of an Evora 400 with room to spare, so having 2 of those as well is an options; or two of the Babyzen yoyos mentioned below. For journeys where we loads loads of kit we have another car with more space. Here is the folded twin pram: