While there are exceptions, very few children train for keeps before 2.5 at the earliest, and boys usually not before 3, sometimes as late as 4 years. Before then, a child's nervous system, his emotional capacity, and his physical ability to recognize and hold an urge are simply not developed enough. Parents who start working with their children earlier than that usually end up angry and frustrated, with distressed and resistant children. Right now you've got yourself trained to get him to the toilet – he probably doesn't reliably recognize the urge in time. And the "training" just drags on, and on, and on….
I'm afraid you may have two problems with trying to train your son now. First, he's probably fed up with the process, and feels like a failure. You may as well be requiring him to pole-vault. His emotional readiness has probably been pushed back a few months by all the pressure he's received so far, so more force of any kind is not likely to help. Punishment or anger from a parent is almost always counterproductive when it comes to any issue of bodily control.
Second, even kids who are well-trained by the time a new baby arrives will often respond to the stress by regressing and having accidents again. So your timing is really not ideal on that count, either. Sorry that the news isn't better, but there is no phase of a child's pjhysical development that happens on the parents' schedule.
Kids really want to train when all their ducks are in a row. When the time comes, training often takes only days, with no more reward than a happy and supportive parent and a new set of big boy underwear. It's as natural as starting to walk or talk when the child is ready. I think you'll be doing yourselves AND your son a huge favor by letting him adjust to his new sibling before instituting any other major changes.
On the sleep issue, you don't say how long till #2 will arrive. If it's less than maybe 6 weeks, I wouldn't force major changes now, or your son may believe he's being rejected in favor of the newbie. And particularly because you haven't been consistent in your approach so far.
But have you considered making up a cozy "special" sleeping spot for him beside your bed, and allowing him to fall sleep there, or join you there in the middle of the night? I've also heard reports from parents who "add value" to their children's rooms by sleeping on the floor for awhile beside the child's bed.
By the way, based on the positive experiences of several young families I know, I think you will like the book "Siblings Without Rivalry" by Faber and Mazlish.
Good luck to your growing family!