Possible to re- sleep train @ 19 months?

We sleep trained our guy at 4 months then had to again at 10 months, and sleep was going okay but now since he turned 18 months the separation anxiety is kicking our asses! He’ll only fall asleep if one of us is sitting in the room with him- this often takes 30mins/1hr and then if he wakes during the night (which he does every night) he’ll cry and scream until we bring him in the bed with us. I’m at the end of my rope I need this guy sleeping better! Is it possible to re sleep trained our at this age? I feel like he’s so headstrong he’ll cry until he throws up:(
Schedule is up at 7, nap at 12:30 normally atleast until 2, then bed no matter what he wants to go to sleep at 8:30. Help!!