I can sympathise with you-- my daughter is 5 and STILL gets up every single night. We just let her get quietly in bed with us. I think she was about 2.5 or 3 when we made a "special bed" for her on our floor. She was allowed to come in without waking us and sleep on her special bed. We made it kind of a big deal and practiced exactly what she would do in the night (have him lay down & coach him to go QUIETLY into your room & lay on his special bed). You could make a rule that as long as he is quiet and doesn't wake you up, he's allowed to come in and sleep on the floor, but if he wakes you up, you will take him back to his room and sleep with him there (or you can give him a choice as to which he'd want to do-- special bed or lay with you in his room. Kids love having choices. Just make sure you like either choice you give him).
This could just be a temporary solution until you get enough sleep that you feel you can take on the task of walking him back to his bedroom at night.
Also, for a while, our daughter DID sleep all night in her bed and I think it was because I didn't lay in bed with her while she fell asleep. I told her early one evening that "tonight, I'm going to read my magazine on the floor while you fall asleep. There will be no talking after the light goes out." I got a book light & sat on the floor by her door & read my magazine-- this helped me be patient while she fell asleep, which sometimes took a while. Yes, she tested the "no talking" rule and she didn't accept that I was going to sit by the door right away. So when we were first trying this, if reminding her there was "no talking" didn't work, I would compromise if she protested-- I'd say "one more question" or "I'm going to read my magazine for 1 minute and then I'll come lay by you"-- but I always started out with sitting on the floor & allowing no talking (and I'd let her know I was going to leave the room if she talked after her "one question." And I WOULD leave the room for a minute or two. Then I'd come back in and say I was going to read my magazine for one minute and if she was quiet, I'd lay down with her). After all this give and take, I eventually didn't have to shush her or tell her I'd lay with her, and the time it took for her to fall asleep got shorter & shorter.
Eventually, she started falling asleep in about 5 min & she would sleep through the night. I think just being used to being in the bed by herself helped her to fall back asleep by herself if she woke briefly. (Long story short, we now have an 18mo & I lay in bed with both until the 18mo falls asleep--usually after the 5yo. So now the 5yo is back to waking in the night.)
Another solution-- have you thought of getting a big bed for your 2- & 8-yo to share? Of course, you'd want to make sure this is ok with the 8yo. If they get along well, this might help. Good luck! Just do what you need to do to get some rest for now, and if that doesn't work for you long term, try something else after you've gotten some rest!