Do not use the share icon for group member adjustions
That is bad as semantically this icon on Android means to open a share menu to share something (a link or so) with another app or user. That is not what it does in this case.
So you really need a different icon. E.g. you could just use the already existent membership screen and just add a button for the admin "invite new user". There is no second button needed at all. This just confuses the user.