Do you have to rock him to sleep for naps & bedtime? Are you rocking him at night everytime he wakes?
If yes, then I would say the rocking has alot to do with the night wakings as well as the shorter nap. Ideally he should be sleeping about 1.5-2hrs during the day & 11hr night so to start with I would do an earlier bedtime. Try to be in cot by 6.30pm so that he catches up on some lost sleep & is hopefully better rested.
At night when he wakes (as well as all other times he needs to sleep... nap & bedtime) I would do some sleep training. I would have a chat to your neighbours (if they are friendly enough) & explain to them that he is not sleeping well & you will need to help him out but you can't be rocking him to sleep either cause at the end of the day you & your sleep (not to mention your son's sleep) is just as important as their sleep.
Here's a link for sleep training for toddlers: -
https://babywhispererforums.com/index.php?topic=63896.0. I would suggest the wi/wo method. YES he will cry at night but by going back to him you are reassuring him that you won't leave him to cry on his own (hopefully he won't get so worked up that he will get sick) & at the same time you will be teaching him how to fall asleep on his own.
Has he always been rocked to sleep? If he was an indepenadnt sleeper in the past, it would probably only take you a few weeks to teach him again....
Have a look at the link & let me know what you think
Layla