OK, while I agree with other posters. You shouldn't get one if you arent sure. It's also normal to have a wobble.
Why does your 11 year old think it will be too hard? And why doesn't she automatically think the older dog won't like it? How much puppy experience does she have?
Surely these are 2 big issues that you have already thought out and decided it will be fine.
Yes, broken sleep is a killer and puppies are exhausting. But it's usually worth it and it's over fairly quickly, in the scheme of things. Were your wobbles serious wobbles or just a bit of anxiety about how much things will change. It's normal to just have doubts or second thoughts. You need to decide which they were.
Is husbands wobbles the same as yours? Again, you need to discover if its serious second thoughts or just apprehension.
Your older teens that are excited for the puppy, how much time have they committed and are they likely to stick to it?
They should be doing quite a bit.
Its really OK to disappoint your kids if you feel getting a puppy isn't right for your family. But it's also normal to have doubts.
You and your dh need to do alot of thinking and talking. And maybe discuss with the 11 year old, about why you don't think those things are going to be an issue (presuming at some point you didnt).