Since UT and OT signs are so similar, he is probably OT now (since you pushed A to the max already), I would cut now. It is nice how his naps are still long enough.
I would squeeze a third nap, even 10 min, or put to bed very early (can be up to 1 hr earlier if needed) as the difficulty going down for the night time suggests. Also it is the time for a huge developmental leap, those wonder weeks, so may be he is practicing that sitting in his head), try to not despair too soon...
NW , can he be genuinely hungry? Sometimes a little snack (one breast instead of full feed for ex. to keep his daytime feed on schedule) can help. But if it doesn't then you can change the strategy next night. Or do a dream feed (whatever worked for you, but it is known that some BF babies regress around 6 months to eat at night).
Let us know how it went, even if all gets back to normal...
Also, you were right to try capping all daytime nap, it works for some, may be once you solve OT you could cap it to something shorter if nothing else works...I would try one thing at a time.