"And his overbearing personality is His personality.Same way yours is yours."
Yes. And no. Everyone on the planet has the ability to be bolshy, rude, overbearing... but the vast majority of us choose not to be, purely because we grasp the fact that being rude? Or overbearing? Or bolshy? Hinders us in so many ways. Our personalities are not something we're inherently born with, OP - they are formed through what we're permitted to get away with during our formative years. Unless your son has a mental health condition, or perhaps a learning disability which you've not mentioned (and why would you?), then his being "overbearing" is because you and his father (although as you've barely mentioned his father, so I suspect more you...) have allowed, perhaps even unwittingly encouraged, him to become thus. There's a very large age gap between your second and third oldest sons. For whatever reasons, perhaps, subconsciously, you thought he was going to be your youngest and did as many of us are guilty of, and treated him thus? If he was spoiled whilst growing up, it's no wonder he's expecting you to pick up his slack. But by continuing, as a grown man with a child of his own, to be "overbearing" is a choice, not by dint of his personality, I'm afraid.
My oldest has mental health conditions and grandparents who have spoiled her. She's the same age as your second son is. She's been employed, consistently, since she was 16... whilst continuing with her education. She was in paid employment throughout a full time university degree, and quite frankly; if she can do that? Then any able-bodied 23 year old can, regardless of whether they have a child to provide for... or not.
Treat your son like the adult he actually is, OP, and one day... perhaps you'll have a son who isn't overbearing, who doesn't expect his Mummy to deal with the consequences of the choices which he has made, who can keep a job and who is raising their child to become a successful adult in their own right, too.
I was 20 when my oldest was born. My ex and I were both in full-time employment at the time, and I took time out to retrain by going to university. We paid our own way, we provided for her - and later on, her brother - ourselves, we didn't expect anyone else to pick up the pieces. Why? Because we were both legal adults at the time, and having her? Was my choice. Yes, her parents doted on her... but as grandparents, not surrogate parents which, if your son's girlfriend and their baby have moved back in with her family, is a possibility. Also... surely he and his girlfriend would be occupying one bed? How can there not be room for them, as adults who have a child of their own, to stay together so that they can raise their baby?
Or, as someone else suggested, does the other grandmother not want an "overbearing" manchild with a mother who does nothing but make excuses for him, actually with her own child? Have her protective instincts kicked in, too, to the detriment of your son's family unit?
Yes, it is very easy for us to say "well, I'd not do this; I'd do that instead" - but a lot of us have grasped the concept that pandering to our adult offspring doesn't help them in the long run.
My oldest no longer lives at home. I made a choice to protect and set a good example to my youngest (who is 14). It wasn't an easy choice for me to make, because she is my daughter and I love her. But she's an adult. She has to stand on her own two feet.
So does your son.
Let him be the adult that creating a child made him.