Well that happened to me too. I think it was something about the inteenimater because when I downloaded the flavour packs the problem just disapeared.
The Inteenimater is not interfering with the ability to propose. In fact, it enables engagement and marriage options between pregnant teens and the father. The No Age of Consent Flavor Pack removes the pregnancy restriction for teens, along with several other teen restrictions, allowing them to function more adultlike.
As far as snowbright's problem, provided both sims are adults or elders, neither is engaged, or married, and they are not related, the only thing that could be stopping any of the proposal options is a bad mod. The ones you've listed should be just fine. A teen in a game without the Inteenimater cannot become engaged or get married. A Young Adult without the Inteenimater cannot get married, unless the YA is a dormie, and a playable sim proposes.