Ideally yes, it must be really uncomfortable for you and when you add a child to the mix it will get more complicated.
Well there is still time for him to seek employment before the baby arrives. I would be accepting the MIL's offer if I were you. No baby needs to be around meth and it's an unacceptable situation for what will be your new little family. It must be hugely stressful for you?
Are you at work still or on maternity leave?