Two male sims cannot get pregnant by woohooing. You'd need a same-sex pregnancy mod to enable Try For Baby, and male maternity wear (from MTS). But this is not "alien pregnancy" (the child will be half-alien though).
Male sims get alien pregnant as a result of being abducted. Once a sim is abducted they get the "Abducted" moodlet for 10 hrs. Once that expires there is a 33% chance of the abducted sim getting alien pregnant IF the sim is male and IF the sim is not an occult (or alien). Alien pregnant male sims get a 2-day "Unexpected Weight Gain" moodlet (which is the alien pregnancy moodlet) right after the "Abducted" moodlet wears off.
The chances for an abduction of a sim from the active household is 1%. To increase that for a single night you can have the household use the telescope and/or collect space rocks. Each space rock collected adds 15% to the abduction odds (capped at 60% bonus odds from space rocks) and use of the telescope adds 14% to the abduction odds. So, 75% total if the household uses the telescope and collects 4 space rocks. That's just for that night (midnight to 3 am). In my experience sims must be awake to be abducted. Furthermore, it's random which awake sim in the active household is abducted (aliens and sims child aged and younger cannot get abducted).
There are mods to increase (and decrease) these chances, and NRaas Retuner can be used to set the chances to whatever you wish.
Not sure about the university test. Usually I can send sims who just have the "Abducted" moodlet to uni since the game doesn't decide on alien pregnancy until that moodlet expires. In fact, you can save the game just before the "Abducted" moodlet ends and reload until you get the "Unexpected Weight Gain" moodlet. Or you can use Nraas MasterController to just give your male sim the "Unexpected Weight Gain" moodlet - that will work too. I think that once a male sim has the "Unexpected Weight Gain" moodlet they cannot enroll in university, but I never check that since the moodlet is pretty obvious. Even if you have NRaas Traveler set to allow pregnant sims to travel, I think alien pregnant male sims will lose the moodlet (and hence the alien baby) if they travel.
edit: once you invite an alien sim over (or move one in, or one visits) the only options available are the default TFB ones between male and female sims. Same-sex TFB requires a mod.
Lastly, alien pregnant male sims don't use maternity wear, they just get fat over the course of the alien pregnancy.