No PhD research group during my PhD. How do I handle it?
Besides the obvious answers (try to move closer to the place where your supervisors and their groups are and meet them more often) I suggest

try to find or initiate a seminar close to your interests.

This would provide a regular meeting point for you and your supervisors (besides meetings directly related to your PhD) and hopefully other people with interests similar to yours. Your supervisors may help to find a theme and spread the word (and probably take formal responsibility for the seminar) but you can and should offer to organize the schedule and the collection and circulation of abstracts.