Sleep gets more sleep. Sounds counter-intuitive, but it's true. The less sleep a kid gets, the less they're going to sleep, which then just compounds an already sleep-deprived child.
I had one bad sleeper that I learned from so that my second was a better sleeper. Between 7-8 months, both had some bad stints for a month or so as teeth were coming in, rolling over got more fun, crawling started, etc.
At 8 months, my second child went to bed around 6pm. But that was after about 4 months of sleep-training to get her to be able to go to sleep that early and sleep until 6:30. My first kid wouldn't sleep through the night until he was about 1 yr old! And I currently watch my 9 month old niece daily and from the time she was 5 weeks old, I enforced consistent naptimes and wake times so that she would sleep right at night, which would then make for good daytime sleeping!
You could try to give him a not-full-bottle in the 4am dark (it's not unusual for an 8 month old to get hungry) and put him right back into bed when he's done. No talking, no nothing. Just functional. Then, at 8-months, he should be getting at least 2 naps a day with only about 1 1/2 hrs of wake time in between. I am adamant about this with my niece (and my sis is very thankful!). Once babies pass the overtired moment, it will be that much harder for them to fall asleep, especially for naps, and thus they get the "bad napper" tag.
I highly recommend Dr. Marc Weissbluth's book "Healthy Sleep Habits, Happy Child". It saved my first child's sleep and helped me get the second on track early on so that I didn't need to do much, if any, cry-it-out with her. Greatest book ever!
Good luck and I hope you all get some much-needed rest!
(P.S. my first is still an earlier riser than the rest of us, but he's moved from 5am as a baby/toddler to now 6:30 as a kid, which is nicer on on all of us!)