Welcome @Maghunter
Neither of you have to start with your call sign. You can just push the PTT and use each other’s names. “Hi Dennis, this is grandpa.”
Every 15 minutes and when ending a transmission or series of transmissions you are also required to ID. You can include some other identifier, which could be a letter, number, name, or pretty much anything you want: “Wrom258 - grampa”, but you’re not required to.
Exactly the same on a repeater.