Ok, so almost certainly your A times need an increase - average for 6 months is 2:45 to 3hr, so it might be best to start there and tweak after a few days to a week, long enough for him to settle into the routine and us to see some real patterns.
There are a couple of ways to do the increase of A time:
1. increase in 10-15min increments every few days - this can be difficult in that it will take a long time because you're starting so far behind where he should be, you can end up chasing your tail because the nap lengths don't mean anything because you're changing so regularly and he may struggle to keep up, so you'll get OT length naps when he's still on too-short an A time because he's simply not used to being awake that long, that will then stall your increasing of A times and cause more issues than it solves.
2. jump to 2:45, resettle the inevitable OT nap wakings for the first few days then watch him for a few days. This is difficult because he will almost certainly wake at 25-30min into naps for the first few days and will be whingey through the last part of every A time because he's so used to having naps so close together.
I think once his A times are more age-appropriate, he will go to sleep more easily simply because he's actually tired.
Moving naps further apart and expecting them to be longer of course increases the time between feeds. What I'd suggest is a topup feed relatively close to the main feed when he wakes from a nap so he's getting topups but also getting hungry enough for a proper feed when he wakes, eg:
5:30 - wake, BF
6:30 - topup BF
7:30 - breakfast solids
8:15 - nap
9:45 wake, BF
10:45 - topup BF
solids if desired
12:30 - nap
2 - wake, BF
3 - topup BF
4:30 - catnap (45min max, try to PD after slightly shorter A time to increase chance of short nap and waking happy)
5:15 - wake, BF (this is then tanking up for night)
BT routine incl. BF
7:30 - asleep in bed
As he starts taking better feeds, you can draw those topups closer to the main feeds and even drop them altogether if possible. If the TT is still in play, he may not transfer as efficiently so they may need to stay.