As much as I like to call it "Snape's Gang" because it's a name easily identifying in the fandom and Snape is obviously the protagonist of the Marauders Era, I don't believe he was the head of that group or at any position of leadership at all lol.
Sure they were friends, and I'm being generous with that term to describe the complicated web that was the relationship between all of them, but they had a very defined structure.
Rosier was probably the "leader" of it, or the closest there was to a main leading figure in the group, with Avery being the closest second in charge. Why? Because they both are pure bloods, AND members of a sacred twenty eight family. Rosier is only slightly above Avery in the hierarchy because the Rosier family is richer than the Averys and he is more level headed than Avery who acts first and thinks later.
Below them it would be Mulciber and Wilkes, Mulciber has a higher ground than Wilkes simply because, again, he is richer than Wilkes and while he can be a little bit brutish by, like Avery, acting first and then thinking later, he is at least directly active against anyone who comes for them. Wilkes honestly doesn't do shit, he can't fight, but he can manipulate people and social settings like an instrument.
And then, there is Snape. Poor, half-blood, spiteful, a rightful bastard but utterly brilliant. They appreciate him like anyone would to a disheveled grumpy feral cat who you can't exactly get rid off because he is useful catching mice (or in Snape's case, a genius in potions and a swot in general with a sick and dark sense of humour all of them found funny as hell) but won't let you pet it without being risked a severe scratch.
Snape was not making any decision in that group, and in times where he was, then they all knew things were very fucked up.