My real advice… start working for him and using the software yourself 100%. Even for $5 an hour so you both have skin in the game. Him to have some help, you to learn, but the money adds a bit of reality so neither of you do things only because it’s free or because it’s family.
My saas has improved leaps and bounds this year when I started to work in the industry for a company actually using my product. I learned things I never saw by just giving demos.
Its really not hard to sit down and listen to users but I have encountered such massive egos and resistances to simple moving a button somewhere else or changing a flow or behavior to be easier to use for a layman that the juice is never worth the squeeze. Often to get the flow that I want to use I just resort to hacking apart the Api bit by bit and making my own horrible layer on-top of the existing solution because i am still standardized but I don't have to deal with politics in making a change request.