Ok, well it's not too big a mess really!
First thing I would do is encourage your DH to stop doing the second DF, the trouble with that is it could be disturbing his sleep patterns and you could be teaching him to be hungry at that time as he will expect to eat then when he maybe doesn't need to. If he has that feed at 12.30, by 3.30 he could well be hungry which is why he's not settling properly and waking a short time later. I would do the DF between 10 and 11 as you have been and then let him wake when he needs to but try and resettle first if it has been less than 3-4 hours since the last feed. If it's more than 3 hours then I would feed and get him back to sleep ASAP.
He is still taking quite small feeds for his age, have you tried a faster teat to see if that helps him take a bit more? It could be that he isn't able to go longer than 3 hours yet because he is having expressed milk, BM does digest faster than formula (but 3 hours is totally age appropriate so it's not really a problem as such!). I would also try and start his day at the same time, you need a 12 hour day/ night so if he is going to bed for 7.30 then have him start the day at 7.30 too. If the 9am start suits you then run a 3 hour EASY so he goes to bed at 9pm (but babies do seem to do better on a 7-7ish routine).
What do you think?
Laura