MeOnFire go into the Clan screen and promote some people.
You can base this on the level they have acheived if you like.
30 Level or more being the half way mark for level 60 maybe.
Select the person x to bring up the choices and then select Promote.
I'm not sure if this gives them the ability to invite people. Might need to be tested.
- Destiny (PS4)
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- MASS Effect 1-2-3 (PS4)