For a simplified case a mediator would work but I think in this circumstance perhaps a lawyer would best be able to protect the children’s and mother’s rights to get a fair settlement. Each scenario is very different so it is hard to say.
This scenario sounds like it can get very complicated.
Yes, because there are children and this H “sprang” this divorce on the W and it’s not clear whether the H is self-employed and has been able to hide assets, I’d definitely want to have an attorney, whether or not it ultimately is a mediated or court-handled divorce. The children are young, especially the 5-year-old. Exes have a tendency to have other interests and obligations in the future and likely NOT to be very focused on the kids & obligations from marriage #1.
^^Exactly what I was thinking. My radar sees too many red flags.