I suppose I should clarify that.
In my game, there are different kinds of characters involved. Perhaps the most obvious are Player Characters (PC's) and Non-Player Characters (NPC's).
I use those as categories for other types of characters.
For PC's, it gets broken down to Active Player Character APC) and Secondary Player Character (SPC). An APC is one that is being role-played by a player during a game session. An SPC is a character that is an equal member of the party, but is handled like a Henchman in all other ways.
Keep in mind in my game, Players only role-play one character during the game. Pretty much in the first person as for the time being, they "are" that PC. All other characters in the game are handled as a chessboard general would direct them. Essentially in the third person.
Henchman and Hirelings are subordinate to the APC in the game. They are beholden to the APC in some manner and get only a fraction of the XP and treasure rewards.
An SPC is handled the same way in terms of conduct, in the third person. They are not subordinate to any other party member but they respond to being asked to do things or for information by other party members or directed if one PC in the party has taken the role of party leader.
The DM (me) will roll dice and otherwise determine how the SPC responds to what's going on around them. I try to keep it as random as possible so that I do not begin to treat the SPC as a PC that I am running. I don't like that because it becomes too easy make unfair use of my knowledge of the game.
The Players at the table, should their APC die in the game, are able to take over any Henchman they have in the party as their new APC or they can ask me to take over an SPC as their new APC. I create quite a few using an online character generator so as to have some ready for just such a purpose.
I do have characters that I have created of my own that I will have enter the game with the party as an SPC. Players cannot take these SPC's over if their APC dies yet they are otherwise handled the same way except that I will allow myself to give them more personality as I imagine them to be (in the third person).
Really, it's only the SPC getting a full share and being an equal member of the party that separates them from the NPC Hireling or Henchman. To me though, that's an important distinction.
A Player that really wants to bring in a second or more PC's of their own creation into a game can choose to bring them in as SPC's instead of as NPC Henchmen. They are required to manage the characters in the same way I do as the DM though meaning they still only role-play one Active PC and I will determine responses and reactions to requests and how they respond to the game around them.
They get the benefit of having more than one of their PC's gaining full Rewards and equal standing in the party and no other Player can claim one of another Players SPC's if their APC should die.
They can only take over one of their own or ask to take over one of the DM provided ones.
So far the players have adapted well to SPC's. One thought that meant their SPC's were all "buddies" until I demonstrated that their SPC had their own mind and, buddy or not, would not just be treated as a subordinate to the APC.
An SPC is different from an NPC in that the conduct of the SPC is determined randomly by dice roll or by reasonable anticipation by the GM. Thus, the GM/DM cannot use the SPC as an agent of the game (or should not).