Question
Can the heir DNA clone their spouse? (I know they would have to be a young adult at the time)
Also just to Double Check you can throw fountain of youth elixirs at people outside the household?
I can't find the ruling about the cloning, but I'm fairly positive that as long as the heir is doing the cloning, as a young adult, you should be fine. I just honestly cannot remember if they also had to collect the DNA, or if a non-heir could do that for the future heir. (Not sure why the heir would have had to collect the DNA since, y'know, just marry the original specimen, but you just never know.)
Also, the age extension restrictions apply only to heirs, so non-heirs should also be ok for the elixirs.
However, be aware that the elixir can cause strange aging glitches where the sim(s) stop aging altogether, unless you restart the game. Then they age for a day or two, and stop aging again (I've personally run into it in the 4x4 Dynasty).