Funny that we have been going through the same things with family and friends, & sorry to hear that your brother can't attend but great news about the baby. You should skype each other on the day!
I have only immediate family on my side coming and my partner has lots & lots as he has a very big family. (& its my mother in law to be that is the nervous flyer too!!! - her and her husband - but she has been amazing- they did upgrade to premium which I think will help to make the flight less nerve-wracking !!)
Some of our friends have been really great very honest and told us straight that its not possible for them, but others have said yes defiantly and then avoid the "booking up" bit! very similar to your situation! We have said that its no problem with us if they are unable to attend as we know its such a big ask. I have found it hard with bridesmaids as we don't want to commit to buying expensive dresses and things if they are then going to be unable to go. A few have mentioned booking in the holiday sales / late deals if something comes up but thats leaving it way too late for me to organise dresses & colours, so i've just said thats no problem with us but I will need to have you as guests. (I don't want to sound mean to them but I think its better all round when everyone is upfront and honest).
Have you had any luck with your friends since? How many bridesmaids are you hoping to have? xx