As long as you remain white I'm sure you will have no problem.

for all its faults - stick with the UK and NHS

No Problem You are white, blue eyes, speak with that funny accent that adds 15 points to your IQ, and have light colored hair. The only thing better would be if you were Norwegian. Trump's racism leans in your favor.

I honestly have no ideas or solutions. I wish you all the best. Hopefully your sons stay close to you, at least in heart and communication. I do have concerns for some people I know here who have come from abroad. One is a Brit I met in therapy group. I don't know his legal status as we never spoke of such things. Another, a young lady, friend of my son and married to another friend has spoken to me of her fears. Even though she is fully legal, married to an American (A lawyer now), and a tenured professor at Temple. She is, however from one of the Prezs "shit countries." It is a scary time here for many people.

I'd contact the American consulate and ask them. You are not black or brown skinned so Trump may let you back in.

Can a UK visitor use their UK national health insurance benefits in Canada? If so, perhaps you could get your meds refilled in Canada, before entering the US?

Worse if you are Brown

You're right about the insurance and meds. Mine take 2/3 of my income
And I'm not on any 'expensive' meds.

Valid concerns .
I have no idea about green cards anymore but I hear that things are tight . I became a citizen on 2005 after 10 yrs here , Bcz I had to .
U are a nurse . U can work anywhere and afford much .
If u are critical care , trauma , or OR /ER nurse w experience , or all the above , u can easily make 125-135 year after taxes . Given that u won't live in a village . Employer provides insurance at reasonable cost and high dedactable . Liability insurance reasonable too .
In trumps America , u are lucky to live in Europe . Is depressing for me to live here lately . Everywhere I look , reasons to be sad .

I think you can find free legal counsel if you look...your questions are Far beyond my scope, and I believe you may have form grounds for worry....sorry!