I think you are right Patrik. Based on my last (frustrating) effort, my statistically insignificant impression is that temple activities have no impact on relationships. I had one temple for each god and no non-denominational temple, so dwarfs with the same gods were often praying together. They did not have an increased frequency of relationships as far as I could tell.
I also burrowed 7 (ish) dwarfs in a separate section and their only interaction with other dwarfs was by bumping in the hallways when hauling. Even then, they managed to form some relationships with dwarfs in the other burrow (though at a lower occurrence level).
I also had separate meeting halls from locations (none of my locations were ever a meeting hall -- I designated them all by making a dining room from a table and making a location from there). Idle dwarfs hung out in the meeting halls, while socialising dwarfs hung out in the tavern. I was not able to distinguish relationships from that, but my impression was that those socialising in the tavern did *not* tend to form new relationships. It seemed to happen more often from dwarfs who were idling together.
Like I said, I had lots of problems with this fort. I gave up because my burrowed 7 dwarfs all seemed to have their history change (they acquired spouses outside of the fortress -- and even children!). It seems unlikely that I missed it when I set up the burrows, but it is possible. Next time I try I will take better notes (and investigate the dwarfs in legends mode).
If I were to make a guess, I think the best way to form relationships is to have the same dwarfs idling together. To do that I would make sure that none of my locations were meeting halls and I would create a meeting hall for the burrowed dwarfs (possibly a small one -- there may be a distance factor). I think I would try burrowing only your 2 candidate dwarfs in that space.
For a tavern, I would make a small tavern, but I would burrow something like 20 dwarfs in the area (and no visitors). One of the things I noticed was that when you have a tavern for only 7 dwarfs, most of the time the poor dwarfs are "socialising" by themselves. You need to have enough dwarfs so that you have dwarfs with needs at the same time. For size, I think I would try making it big enough for 4 dwarfs -- so max 8 tiles? Big enough that they don't fight, but small enough that they have a good possibility of being in adjacent tiles while socialising.