You're already stressing out, and feeling anxious about the prospect of getting on a 'plane. And now you know your daughter is due to give birth to her first child just after you return. Frankly, it doesn't sound like you're going to enjoy the prospect of being away from home, and possibly not being around if the baby arrives early. After travel, you would no doubt have to wait a while before safely visiting your daughter, and new GC. I personally wouldn't want to be away when my daughter was due her first baby, and I know that my DH wouldn't want to be either.
You say that you and your DH have been staying home, and hardly seeing anyone ... do you really think things are going to be so massively different by October, that you'll both be happy to hop on a 'plane, and enjoy your travels? You should speak with your husband to find out how he really feels, now that your daughter is pregnant, he may feel the same as you, or he may be adamant that he still wants to go, and he'll be upset if you cancel. You should explain to him exactly how you feel, and hopefully you can make a decision together.
I've got another 'keen'... Ouch!