According to the OP, his house is not very secured and he's thinking of memorising his recovery phrase well it's a bad idea because the disadvantage is much greater than the benefits, the human brain was created in a way to store information given to it for a very long period, well not everybody has retentive memory and it's normal to forget, if the OP is one with a retentive memory then good for him and the benefit is that no one else can have access to his wallet asides him but the bad side of it is health issues like Amnesia, severe Typhoid or as result of stress and he could lose his assets completely if such occurs and he's not able to remember even if it's a word from his recovery phrase. I support your idea of telling him to strore it in an email supported by 2fa or he could as well get a safe and store the recovery safe written in a document inside it.
Reading this was very funny to how op said his house is no longer safe then were exactly those op thinks it's safe and memorizing it is even worst than him complaining that his house is not safe, what if you forget how do you get back anything back. The disavantage of mesmerizing is more than that of the advantage, so why put your funds under that risk just because he feels his house is not safe. No matter how intelligent you are or even have a retentive memory I would not advise anyone to try and store something of valuable in your memory.
And if op thinks he can actually do it then I don't see why we should even be worried about him is an adult and I think he should be able to handle is own problems, some situations are ment for the person to learn the hard way op should be left alone eventually if he succeeds then congratulations to him and if he does not succeed then to is lost then.