The Totem Barbarian's Aspect of the Beast, Elk aspect increases travel speed by double. If two Totem Barbarians both with the Elk aspect were traveling together, would their traveling speeds double a second time?
\$\begingroup\$ Does my answer solve your problem well enough for a green check? \$\endgroup\$– Thomas MarkovDec 30, 2021 at 12:10
Game features with the same name do not stack.
In the section Combining Game Effects of the Dungeon Master's Guide, we see:
Different game features can affect a target at the same time. But when two or more game features have the same name, only the effects of one of them—the most potent one—apply while the durations of the effects overlap. For example, if a target is ignited by a fire elemental’s Fire Form trait, the ongoing fire damage doesn’t increase if the burning target is subjected to that trait again. Game features include spells, class features, feats, racial traits, monster abilities, and magic items. See the related rule in the “Combining Magical Effects” section of chapter 10 in the Player’s Handbook.
This means that a creature can only be affected by at most one instance of Aspect of the Beast (Elk) at a time.
It is worth noting, however, that Aspect of the Beast (Elk) and Aspect of the Beast (Wolf) work together just fine, so you can double your pace with Elk, and with Wolf, you get some good benefits for traveling:
You can track other creatures while traveling at a fast pace, and you can move stealthily while traveling at a normal pace (see “Adventuring,” for rules on travel pace).
Anything with the same name doesn't stack. (unless it says it does)
This is most notable with spells, but class features also work like this.
However in this case the Elk totem barbarian feature is one of the weaker barbarian primal path choices, and rarely sees play. Two characters with that same totem implies a shared backstory, and the benefit of the two features stacking is cool and interesting but not powerful. As the GM you largely decide how far away things are from each other. Players being able to travel overland faster may be very useful to them but it doesn't help them murder enemies which is the focus of the game.
In general any time players are doing literally anything that isn't about gathering power to murder enemies faster this is something to be celebrated as a GM and should be rewarded.
Ergo I would not hesitate to immediately houserule the Elk totem to stack with other Elk totems to increase overland movement speed. I'd probably cap it at something to avoid an entire tribe of barbarians being able to teleport, but, i'd be fairly generous with that cap (like 10x, say). Tribes that live in the wild, nomads etc being able to almost instantly cross vast distances is a common fantasy trope and actually fairly historically accurate - non-nomads thought such travel times were absolutely 100% lies constantly throughout recorded history.