If you are trying to heal out-of-party players in FATEs, go to your character config options and look in the "Filters" tab. There is an auto-filter that makes it so you only target enemies/npcs while your weapon is out that is preventing you from targeting players. Just mess around with the options in there until you find something that suits you.

Keep in mind, even if you do enable the manual filters, the auto-filter will override them when you pull out your weapon and put it away so you will have to disable the auto if you want full control.