definitely watch them, particularly at feeding time
but I've found other issues as well
some snakes, even garters, don't do well living with others and will not thrive, even if they're the same size
one of my garters, who had been housed by himself because his dietary preference was different from his siblings, started doing not so well, when housed in a larger enclosure with a male from another garter species, approximately the same size, who was previously housed with another male who suddenly had grown much larger
by "not doing so well" I mean that he started having a series of difficult sheds and his appetite became lessened
he clearly didn't enjoy the room mate situation, so now he's solo again and eating better