Most people won’t be comfortable staying with inlaws (be it husband or wife) unless your inlaws are gold and treat you way better than their own child which is super rare to come by. Because at your own home, you get to be the real you while over at inlaws, there’s always a mask regardless of how good you’re with your inlaws. It takes only one small thing to trigger your inlaws.
Standing at your POV, I also understand how it feels for your spouse to keep going back instead of accompanying you at this crucial period. Maybe talk to him like maybe comprimise to weekends since you’re gonna give birth anytime and you prefer him to be around so you feel safer. (Let him feel good and needed).
Most importantly don’t compare as it’s a rather sensitive topic. His brother may not always go back to his parent’s place, but he also may not be home to accompany his family. He could be out hanging out with friends and etc.