How do I get my son & son-in-law (2 wonderful men, late 30s) to come back together & restore family peace?

They were like brothers, but over the last few years, perceived and/or real slights, etc., have slowly driven them apart. Since we're a close-knit family this affects us all. With the holidays approaching it's going to be difficult. They have each made mistakes yet each feels he is right & neither will make the first move to repair the relationship. I feel like this is an issue of pride on both their sides. What can a mother do, if anything, to restore family peace?