Need some reassurance!

I'm getting ready to sleep train my 5/28 guy through his nighttime waking. He already puts himself to sleep for naps and bedtime and is a good napper. He gets about 30oz and 3 full blw meals every day.

However, he's been waking around 1/1:30am and screams until I come rock him. It usually takes 1-2 hours for him to go back down. I'm exhausted. On top of that, the last two nights, after I put him back in his crib, he'll wake up screaming again in 45 minutes to an hour and not stop until I rock him AGAIN.

We've decided to go with extinction since he's a little older and he stays laying down crying until he hears his door open and sits right up and won't lay back down. We did this with my now 3 1/2 year old when he was 7 months and it worked great. He is still a great sleeper.

I know we need to do this, but it breaks my heart to hear him cry and I'm afraid he's going to wake up his big brother.

It also feels cruel to do this while he's teething. He stops crying right when I pick him up so I don't think teething is the culprit.