Life is too short to allow such conflicts to dominate a family’s life. Better to mend fences now than try to do it in the midst of some crisis.
Try a face-to-face meeting with relatives that disagree, and request that neither one speak until you have finished. Then you will be ready to listen to each one.
If they won’t do that, try separate face-to-face meetings with them with the same request and promise as above. In the last resort, send them identical letters communicating what you would say face-to-face if that were possible.
Keep in mind your efforts may not succeed. You will, however, be able to live with yourself more easily once you have formulated and carried out a reasonable plan to dislodge this conflict from its current stagnation.
Above all, keep praying!