18-24 months for your wife’s mother as there’s no numerical limitations on the number of visas that can be issued to immediate relatives of US citizens. I do not think the situation you described qualifies for an expedite; usually it’s the petitioner whose circumstances come into play for an expedite. But of course it’s free to try.
For the brother however, since he is not an immediate relative, by law there are numerical limitations on how many F4 visas are issued per year which created a massive backlog. It’s about 20 year wait which probably will only increase with time and it’s not possible at all to ask for any expedited or any exceptions as again, it’s just not possible as the law caps how many are issued a year and you just have to wait for your visa number to become current (~20 years).
A little quicker way would be for the mom to petition for him once she becomes an LPR which would take 10 years at the very least. Again, this is due to numerical limitations set in stone I explained above, this time the category is F2B and he must remain unmarried.
There’s of course a bigger issue of self harm and mental health issues that come into play at the immigration medical down the line once the interview is scheduled. If he is deemed a danger to himself or others he will be inadmissible and will not be able to receive a visa and immigrate.
You have to rest each and study the visa bulletin and how it works. Start googling and reading up on it, that determines when a visa nubs be becomes available.