Your example is a bit complicated. I would definitely agree with "latter two" if the latter two in question are singular (though "last two" is better - I normally only use "latter" to mean the single last item, in this case, the eight health care assistants); for your case, I'm half tempted to say "latter ten" (but, again, it should really be "last ten").
More seriously, "the two last groups" (or "the last two groups") would probably work better. I'd rather use "the two latter groups" over "the latter two groups", but IMHO both are worse than the versions with "last".
Incidentally, you do not need a comma after "latter two" (or any of the clauses I proposed), and not after "they include" either (though a colon would work).