Relationship yes, marriage no. The nearest is the Story Progress telephone-call with ring in the bag (engagement-call). Maybe someday they will add marriage to Neighbourhood Stories/Phone-NS-Call but for now you need to play these sims if you want to marriage them without cheat (cas.fulleditmode)
For relationship should be under friendly -> Ask/Talk about Another Sim… -> There is one for you want that these sims get friends/date with... (Because of EA-App I can’t switch language anymore, so I don’t know how exactly the sentences are in English). The chance should be 50% that they after this are a couple. (They need to know each other for it!) <- I am not sure if you still need Get Together for this or if they add it in the base game.
I agree with simsplayer, the easiest way is just to add a new created NPC. If you marriage them in CAS with cheats (cas.fulleditmode) they will not have any romantic relationship which is a little odd, if you ask me!
Neighborhood stories miss a lot of features for a true story progress, especially if you play with aging on for unplayed NPC. Because of this many pc player still use MCCC, this mod has these missing features (Townies can have romantic relationships, marriage, cheating which create more babies, divorce)
Talking of neighbourhood stories I've had to turn that off as it was causing too many bugs. But yes the marriage and have baby effects still take place in households with established couples or with dating couples. One of the bugs I still get is that answering No doesn't always work and even if I'm playing a Sim they sometimes get engaged after a call from their partner even if I dismiss the call. Saying no to babies resulted in a household full of babies and some elders getting pregnant too. I think it was meant to help with things like this but for me it's too buggy and intrusive. I've reported the bugs along with other players so hopefully it will improve over time.
