Wow! This went well in the end, didn't it?! What wonderful news!
Re: looking like and telling.... I know ONE child who looked like her dad from the beginning. Newborns change dramatically into toddlers, who often look NOTHING like the adults they will become.
So don't get ahead of yourself there. These children will become so familiar to you, you'll wonder what you were looking for. They're going to be perfect and perfectly themselves.
We hadn't really planned on telling but DD's blood type came out 'wrong' and not what should have been possible. (Donor info was wrong) I've 'told' her maybe twice a year from the time she was about 18 months old. She's 6 now and can't really understand it all yet. I do worry sometimes that she'll tell one specific friend of hers, a girl who I think has the potential to grow up to be a 'mean' girl. So far, she's been very good at understanding that some things are private.
I think telling early helps ME to tell her as there's not a big, heart pounding workup to telling that way, so I can do it somewhat matter-of-factly.