Syzygium oleosum is not a huge tree in the wild, quoted at 8 to 15 m. They should slow down after they grow into 30 to 50 litre pots.
Don't let the root get into the soil thru the bottom of the pot, they will take off again.
I have not seen too many in the wild here in Australia, only ever saw a few in the NSW rainforest, mainly just off the beach. They weren't big trees there.
Other Syzygiums can get a lot bigger.
Are you sure they are oleosum, they are fairly similar to paniculatum, australe, and a few others. Easy to tell apart when in fruit, a little harder from foliage alone.