I.G.
Well, sleep talking is pretty common in kids (up to 50%) and so is frequent night waking, sleep terrors, nightmares etc.
I would suggest that you talk to his pediatrician about your concerns. Sometimes issued like the ones mentioned about have underlying medical causes that can be treated, such as sleep apnea. This can especially be that case if you feel like your child is not getting enough sleep, is not rested when he wakes up.
If your twins are still sharing a room, you may want to try seperating them. Maybe he is a light sleeper and the presence of his brother disrupts his normal sleep phases.
You doctor can order a sleep lab observation for your child to see if there is any reason for concern.
Most kids outgrow their sleep problems by the time they enter school or adolescence.
Good luck.