In general, the primary person responsible for interacting with new guests is the person who brought them. Bringers should not abandon their guests unless they are satisfied that others have already engaged them. New people should not be left alone during social times before or after meetings.
However, most bringers are happy to have others in the home church talk to their guests, either together, or even instead of the bringer. This could be because the guest is a different gender than the bringer (especially in singles groups), or because the bringer has already made progress, but would now like to have other voices confirm what they have been saying. Typically, other members from the same cell group as the bringer should feel special responsibility to follow up guests. Those from the related men’s or women’s cell would be equally suitable. If a bringer wants others in their cell group to help follow up with a guest, the best thing to do is let them know of the need beforehand.