Just a note to give you a heads up about guys like this. Set a definite timeline! You said you are giving him a couple of months to return the car, but he just might drag it out as long as he can. The same goes for other issues as well, such as what to do with the house, and the divorce. If he is anything like the guy I'm with, a couple of months will turn into a couple of years. I'm kicking myself because I didn't set any definite dates for any issues, and he has dragged everything out, and used my leniency to sneak in paying off ALL of his debt. Now, I'm worse off than when I started with him. Don't let this guy do this to you, please. I suppose you could wait until you feel ready to deal with the issues (after the birth, maybe), but don't allow him to set the timeline (which I'm sure he won't anyway)
Also, I can understand your annoyance with your grandparents butting in, but I think his behavior is unheard of for people of an older generation. I think they are of the mindset that you reap what you sow. You accept the consequences of your actions. Be grateful you have strong people who love you so much.
And, with the evidence of him making many new girlfriends. Don't let him think it's party time. Nope, it's time for him to WORK. Does he have a good enough job? I sure hope so. Don't be afraid to be a little 'mean.' Don't worry if he's gonna call you the 'B' word if you stand up for yourself and baby. Only weak little boys love to use that word to describe women when the women are asking them to do the right thing. Geez, how dare us expect a man to have good morals and values. Please don't feel sorry for him. He'll either not learn his lessons and keep repeating the same mistakes, or he'll eventually redeem himself. He's a grown man, he can take care of himself.