D.T.
Are you still trying to put him in the toddler bed? I would suggest to put him back in the crib and either get another crib (I know it may not make sense monetarily) or use a bassinet or pack and play for the new baby for a while and maybe trying to talk to him after the baby is born about babies needing the extra railings and security so they don't fall out and how big boys sleep in big beds like their siblings and parents and get him to like the idea of sleeping in a big bed over the course of a few weeks and suggest he try it out even if just for naps. I think things are changing in his world rapidly and he may be trying to control what he can. If he thinks that this is his idea and he get to make this choice of moving up he may not resist as much.