Firstly, congrats to Jacob on joining the air force, and good luck to him for his assessment day thingo. .
During his training he should be able to request leave as you can do that for exceptional circumstances, and I would think they would consider the birth of your child to be an exceptional circumstance, though it would probably be in his best interest to tell them in advance. Well anyway, thats what I got told when I applied to join the Army. And he might go to his training earlier. They hold the recruit training many times throughout the year so he could go to an earlier one maybe.

I think you should get your mum there if DF cant. I find it a bit funny that she wont be there to support you.

And having a family member there isnt compulsary, but it would probably make things more comfortable for you.