I.M.
Hi B.. I hope I have some good advice for you.
First off you say you have tried many things. Here lies the problem I think. You need to pick ONE way and stick with it. So if it works, and 2 weeks later he reverts back to waking in the night, use the SAME method to get him back to sleep.
When he wakes and says things like - up - say, sorry, it is time to lay down now - do not pick him up. Rub his back, talk to him softly, leave the room. He WILL cry, so go back in and say it is time for sleep, mommy loves you, you are a very good boy, I will check in on you in a few minutes.
Go back in a few minutes later as promised, and repeat. He will eventually fall asleep. It may take 2 hours the first night you do it, so be prepared and do NOT go back to your old ways of sleeping with him if you want that behavior to change. You can even go in a few times and then say - mommy is going to sleep, love you, see you in the morning, and then leave til morning.
If he says mommy's bed - say mommy's bed is for mommy, this is your bed, time to lay down and go back to sleep.
If he wants you to rock him, say - lay down I will rub your back for a minute and then I need to go to sleep.
When he wakes at 4am, let him fuss. If he gets hysterical (I for one cannot let my LO be hysterical), go to him, comfort him, say it is not time to get up yet, and leave. Again, you may have to walk in and walk out several times - maybe even until it is time to get up.
Give him a blanky, a stuffed animal, and let him fuss for a bit.
Once you get this squared away you can work on getting him to sleep in later. I am not sure what time he goes to bed, or how his naps are going, so it is hard to give advice here, but most toddlers at 20 mos sleep 10-12 hours a night, and nap 90 min - 2.5 hrs - a wide range I know, but hopefully that gives you a base to work with.
Do you use room darkening shades to keep the light out? The sun rises very early in the summer months. Or use a fan to drown out the noise of the birds chirping at 5am?! Try both of those to get him to sleep in later.
Remember - pick a method and stick to it for naps, bedtime, night wakings, early wakings - for all sleep issues, so if they arise again, and you use the same method, he will know what to expect.
Good luck!