This is incredibly stupid.
None of them or her ex, no other way.
The first one cannot get it up, the second one has a history being a cheater(could be slander), the third one is a lover with her best friend and the last one is an ex with a habit of breaking an engagement off.
Assuming she has standards then #2 and #3 are off and only 1 and 4 are options.
The first just has a dick problem so fix it or no, while the other one will either work or immediately call it off.
Last one seems like the best and only option.