Don't worry about the Travel History refusal. It's not possible to change the situation in the current circumstances.
Quite honestly, your mom-in-law (and also your dad-in-law) have good applications.... but the purpose of visit (to take care of your wife and baby) have made their TRV approvals a bit difficult. Also, if they reapply pretty quickly, their new applications cannot state a significantly different purpose of visit. That's why I suggested inviting another female relative if possible. - Yes I agree and understood your point.
You will also need to submit your bank statement (although it is not mandatory for the host's financial documents)