"Anyway she has no idea what her rights are in related to the company if anything were to happen to him or indeed if he has to give up work due to ill health . "
A bit of marriage guidance coming up. Trying to work out her rights on an internet forum is going to achieve nothing other than some vague possibilities. In a small company, the main man is key - without him, the business will struggle.
Going back to my own parents, my father was the most ostrich like man you could ever hope to meet. If he did not want to deal with something , he did not deal with it. End of.
Over the years, my mother developed a series of techniques she would employ on him to try and resolve various, serious issues. Think insolvency, losing the family home, losing the business.......
The techniques:
Reasoning, pleading, sobbing quietly, the silent treatment, more reasoning, opening brown envelopes herself, locating paperwork herself, taking her own advices from a saintly accountant and, ultimately, taking over the family finances while letting my father believe he was still in charge.
The OP's friend needs to deal with the ostrich husband - him changing the subject won't wash. This needs to be a proper, adult conversation without the distraction of the young children. If it helps, having a trusted friend/third party can be brought in.
People can drift on like this forever ( until the ill health gets him) but it is not good enough when there are family and business issues at stake.
mf