Hi K.,
start this on a weekend day when your husband is at home, Have your husband chase your son around the house all day, tire him out thoroughly in a pool, in the bathtub, chasing him through the backyard with a garden hose or jumping on a trampoline. Talk to him about sleeping in his own bed that night.
Then as a first step I would relocate the evening into his room. The reason you are probably in your family room because he or you can watch TV there. Tell him what the last show is he can watch and then firmly relocate to his room. There you start an appealing bed time routine, where you dedicate time just to him that can including doing a little game of his choice, then putting on pyjamas, then reading a bed time story, then brushing teeth and then tucking him in. When he is in bed, you could talk to him a little bit (whispering with the lights out) about what exciting things you are going to do in the future (start with the next day, but gradually you could take this time to talk about what is going to happen before and after you give birth). Then I would install glowing stars over his bed, so that you can tell him to look at those after you leave his room and shut the door. When you are out, please don't have a loud TV running so that he can hear it.
When he starts to cry, go back in, rub his back and tell him it is bedtime. If he gets up, tuck him back in and tell him its bedtime. You will need to let him cry a little bit, but it is easier to handle for you as a parent, if you increase the time that you let him cry gradually from 30 seconds to a few minutes. And under no circumstances I would give in to any whiny requests like have to go peepee or need a drink or whatever. This is bedtime.
I would worry about him getting up and sleeping with you, once you have the going to bed routine firmly settled in his bed.
You need to do this for your own sanity and his and I know you can do it. I am not going to wish you luck, because all it takes is your determination. Picture a nice evening on your own on the couch!