i have twins, now 5. the comments are never ending but generally you will find its people just trying to make small talk, they dont really mean anything by it. you just have to have to learn to take it as a compliment even if it isnt:
Them: i'd hate to have twins
You: (big smile) god job its me not you then, i love it!
Them: Are they natural?/Did you have IVF?
You: Does it matter? (this really floors them - my twins are not IVF but i still think its awful to imply IVF twins are 'not natural')
Them: Are they identical?
You: No, we had them tested to be sure (even if you didnt)
Them: double trouble
You: and double the love/fun/hugs
Them: which is the good twin?
You: today it's A as he ate all his lunch but I expect it will change by bedtime.
Them: Are they twins?
You: Nah, this one's the stunt double
you see, there is always a way to turn it into a compliment/jokey situation.
9 times out of 10 comments are meant in a nice way, honest!