You might be overthinking this a bit, but that's totally normal when you're deep into a project and every word starts feeling like it carries the weight of the whole setting. If your goal is something that sounds prehistoric without dragging in modern associations, then "remnant" really does hit a sweet spot. It's clear, evocative, and doesn't force the reader into any specific cultural frame. It also reinforces their situation without needing extra explanation.
"Pack", "troop", "clan", etc., all carry baggage you clearly don't want, and inventing a new term would probably pull attention in the wrong direction. "Remnant" gives you flexibility and tone while staying invisible enough that readers won't trip over it.