I have twins, had ds, then dd, then came dt, ds was 5 at time, dd, was 3. Jump from 2 to 4 meant, new car, new pram and buying new to double up on most of the other big items, cot (after initial top/tailing), highchair, car seat etc, didn't really have anyone to borrow from. The doubling of cost does hit hard, nursery, clothes shoes, clubs/lessons/activities, party gifts, birthdays/xmas, uniforms, mine are 11 now and school trips is a killer. Trying not to think about uni.
So from a financial pov, I think harder, from coping pov, I think different fro everyone based on behaviour/health/how you cope etc. I'm lucky as mine were also very easy as babies/toddlers, so my own experience probably better than some with twins, having been through it with easy babies, my heart honestly goes out to anyone who has it harder (twins or not). I remember coming face to face with a woman in Mothercare, b/g twins same age as mine, same pram etc, thought it was really funny, mirror image and all, we started chatting...obviously apart from general tiredness, I was really enjoying those early weeks, and she was having a horrible time of it and was barely coping, I just wanted to give her a big hug...