My dad is getting up multiple times a night and believes it’s morning even though it is dark and only 2:00 am. Suggestions?

Ask doctor for referral to a sleep specialist. Your dad has problems with staying asleep. There are prescription medications that can help him to stay asleep.

Also, many Alzheimer's patients have problems with day/night in advanced stages of the disease. It might be helpful to hire a sitter for the night shift who can redirect him back to bed or keep him from waking mom.

Along w/ the other good suggestions you've been given, a weighted blanket might help (you might check w/ his doctor to see if there is any reason this might not be a good idea). The general weight recommendation is 10% of the person's body weight, though my mom is obese and and 11-lb blanket seems to be helping her somewhat. (I didn't want to go heavier b/c I didn't want her to have problems picking it up).

Also, I don't know if a digital clock with AM / PM indicators would help him. We got my mom one the size of a tablet that has the day of the week, the date, and AM / PM time. It has helped her a lot keeping track of the day of the week and with taking her meds.

AD disease affects the person's circadian clock. Although he says "I know", he may not realize what time it actually is. He gets up at 2 or 3 in the morning believing it's time to start the day. There is danger in him doing this. What if he should wake up at three AM and decide to leave the house? Securing the doors may not be the answer, my wife left thru the window! Have you taken precautions to prevent this? My wife left the house one early snowy morning without my knowledge. I awoke to find her not in the house. It scared the dickens out of me. Fortunately, I was able to find her by following her footsteps in the snow. Events like this, and the inability for me to get any sleep, caused me to look for a care facility for her. So be aware that AD is a progressive disease and begin to discuss plans for dad's care now rather than later.

We do not let him take any naps. Exercise is hard with the winter cold and staying in because of COVID.

My husband (81 with Alzheimers) has "Sundown Syndrome" and he's up and down all night long. I find feeding him a heart snack at night helps him sleep.
It's exhausting for the caregiver - I empathize with your mom.

Does your mom go to bed early with him? If not, can she? It might be easier for her if she were on his schedule. Of course, it would be easier if he would stay up later. This is very common. He probably only needs X hours of sleep and when he wakes up, he's up. Kind of makes sense but doesn't work real well for the "normal" schedule. Maybe make sure he gets exposed to sunlight in the morning to let his body know it's time to be awake and helps with natural melatonin production.

If he's napping during the day, try to keep it to a bare minimum. At the time he usually is konking out, try to get him to be active? Going to be a struggle.

Is he getting any exercise during the day? That could help.

I think that the biggest challenge is getting him to stay up past 7:30. He has 8 hours in at 3:30, so he is feeling like it is time to get up in the middle of the night.

My personal experience is that a senior either sleeps to much or they are bright eyed after 5 or 6 hours.

I would find something that stimulates him and keeps him up until 9 or 10 so mom can have a good night's rest. He obviously only needs about 5 to 6 hours of sleep. Oh, and no naps during the day.