What I can suggest you its, you take that 2 kids and yourself move 2 weeks somewhere else, let him finish that 2 weeks in house alone. If he shoot himself, that is his problem.

You help him to say, if that two weeks, how he feel alone inside the house, without any noise. You writing better, you concentrate better, you lazy better, you finding the food better?

You made something at least he has some snacks, or some purchase things settle him 2 weeks, he is Royal life too long....

You set some steps for him and for you. 

You come back and talk about it. 

You are an adult, and you are involving with the Kids 2 in their future life without the supports, I assuming Harry dad or brother making clear on that, or Congress?

There are the story of the China Royal 1911. There were. 

If I were you

I will stay a little while but keep in touch the jobs, or works forces. If I need to. You help Harry to settle in that new enviroment, including all the back-up plans, he can keep that house from the money, or something for the kids, in case he thought about money money money...you find him a better location, get used to that life in California....but if you breaking off 5 years, he won't have a US Citizen? 

Do they tell you if he fails his US citizen, he lives where?

When the kids passing certain months, it may not be long, you watching them, if you wish them well, you finding some of this Epi Genetics like Dr. Bruce Lipton. You see if Harry willing to last a little long a good behavior, just for as little time as you will be together.

You set off your plan on your career with that 2 kids, might be back to Toronto if you were....

You prepare things for Harry. You set his life in order, whether in the US or in England, you doing all the paper works, you finding the resources, you call on the phone, you making some connection.

Including if the kids growing up, you sometimes cared for his diets, his needs, sometimes just sent him some nice blanket, nice gifts wraps, nice home made food, or some preparation he feeling that is his original home. You set up some bar from him to the kids, but you will be running all that yourself....and make sure you telling him, that life how to be responsible alone, don't lose that touch, for you do care that image, or some feeling for him.

He doesn't look like anything achieveable, will soon reaching 40. Your sister-in-law, they are too unhappy on their own, practically if the worlds having any support, it will never be them, or anyone. That life after, its I say so, not you say so, you understand?

Kids lifes are not meant to be ruined, or else you suppose to drop it the first day, no matter what.