Why doesn't my brother sleep at night?

My brother has Alzheimer's and lives with me. I am "it" for his caregiving. I am noticing he is up thru the night when I do "bedchecks," which is usually 12 then again at 2 or 3. Yes I no longer sleep thru the night. I can find him walking around or just standing somewhere, up against a wall or in a doorway. If I was to disturb him he becomes agitated, he wants nothing to do with my suggestions of sitting down, let alone going to bed. Trying a set bedtime schedule did not work, "No I'm not going." I do disconnect the tv at a reasonable time, 10, he is usually asleep on his couch, again I do not awaken him, letting him sleep as much as he can. It's disturbing and sad to find him sleeping standing up against a wall or on the floor with his pillow. I've learned to accept it, realizing it's needed sleep. I also do not want to cause agitation, which has been ongoing since day 1, due to his past dynamics with me. Do you think it would be less disturbing if I had a baby monitor or camera system, just visually checking versus actually witnessing? That's been suggested to me by medical personnel. I must add that finding and keeping care has been a challenge due to his behavior and needs, they must be knowledgeable and willing to go the extra mile with him these days. What a relief for me when a.m. care is here, how sad when they do a "no show," or I hear, "Not for me." My apologies for venting. Thank you all for your attention and suggestions!