All the suggestions made are important in having good relationships (basically treat everybody with respect and personal interest)
However, if each subgroup simply repeats its maximal position, in increasingly strident terms, the outcome is fairly predictable. If there is any desire to reach a mutually acceptable agreement, then someone needs to be the first to invite the other to the table. If one side feels that they cannot achieve a mutually acceptable agreement which meets their minimal requirements, then each side has to figure out what’s its best alternative to a negotiated agreement. I’m afraid that won’t be pretty.
bsorot tovot