I feel so bad for you. Yes it’s true that you probably can’t cope with both and no one should expect you to. Your husband should be helping you. Whatever his work is, it’s nothing compared to the post birth time, breastfeeding every 2 hours when you are not getting much sleep and your body is trying to recover.
I don’t think his parents are helping if they are making comments about you not being capable.
All I can say is just focus on your children and only do whatever you can manage. Just ignore their comments and attitude. InshAllah when the baby is a bit older and you are back to being able to cope with the kids and the house duties things will improve. I know it’s horrible to think that when you need your husband he’s not able to or unwilling to help or at least cut you slack but I don’t know what to say about that.