I think "welcoming someone in" could be just as it implies. Currently my LTR and I are seeking but we have our understanding that we want a relationship for each of us separately just as much as we want someone to share. The dynamic should be that the "welcomed party" should be as comfortable dating each separately as they can be together. I don't think a dating together dynamic would always work because being attracted to the couple together can be so different than being attracted to the single parties.
Maybe I'm not making sense but I know I would much rather our future girlfriend date us separately to get to know us because when together couples tend to have a couple dynamic. Ie: same interests, same foods, music, points of view. Meanwhile, individually they exhibit their true colours. Like together C and I like old school rock/folk music from the 60's-90's but separately I like chill out music like the Grateful Dead and Sublime. He does not share ALL my likes. Nor I his.
Therefore, the "welcomed party" has to like us as individuals as much as we should like them
Hopefully this makes sense.....