Need help to create a custom event

3F XX YY is add character XX to party YY (If that doesn't work, try XX and YY the opposite way, I mix it up sometimes).

You've got it right, character XX to party YY.

Don't forget your characters need properties too! Take a look at Locke's character creation so you understand the process. It just so happens it comes right after loading a map if you wanted to take a look at that too!

Code:

CC/A61B: 6B    Load map $001E (Narshe, all non-shop buildings except classroom (always)) instantly, (upper bits $2000), place party at (64, 33), facing down
CC/A621: 40    Assign properties $01 to character $01 (Actor in stot 1)
CC/A624: 3D    Create object $01
CC/A626: 37    Assign graphics $01 to object $01 (Actor in stot 1)
CC/A629: 43    Assign palette $01 to character $01 (Actor in stot 1)
CC/A62C: 45    Refresh objects

There is a little bit of leeway on the order in which you do each of these tasks, but I try to stick to what the game does. If it doesn't work, try moving some stuff around. I've found that (45 Refresh objects) is sometimes needed, and sometimes not, but I throw it in after every major chunk of changes to make sure the game is keeping up.

Once you've done this for all of your characters, you can add them to your party with the 3F command like Lockirby said.