Its going to be almost impossible to potty train him if his mom isn't also trying
I feel like kids will get the concept in 3 days but potty training doesn’t happen in three days. There will be lots of accidents that require cleaning up after. Very frequent potty breaks. I personally wouldn’t attempt that while heavily pregnant. A new baby can cause a regression in your progress and if mom and dad aren’t on board then it’s kinda hard.
Its a nice idea, but realistically, this is not going to happen. A collapsible step ladder for him to climb up to the changing table that gets put away after is probably your best bet.
My bf and I had potty trained our kids together when we first met. It was a lot of me doing it cause I was home with them most while he worked. His kids were older 3 and 4 (almost 5) my son was 2. It was hard since there mom wasn’t continuing it on her time so they would come back again having tons of accidents. I’m now potty training our 2 year old and I’m 32 weeks pregnant and it’s exhausting but being consistent is the key part. I wasn’t able to do it in 3 days with an of them. Right now I do only underwear at home and he’s got peeing pretty much down, it’s just the pooping🙃 when we leave the house I put a pampers easy up on him and go constantly with him. We’ve been training for 2 weeks and still not confident leaving the house in underwear.