The term interlopers refers to those who interfere in the affairs of others. This term takes different meaning as the story unfolds. In the beginning the two men refer to interlopers as anyone who might try to stand in the way of them killing each other. Later, after the two men are trapped under the tree, make peace, and end their families' feud, they refer to interlopers as anyone who might try to stop them from making peace. In the end of the story, it is ironic because it is the wolves who become the interlopers and because it is the wolves instead of men, the feud continues.
The wolves, because they were unexpected, and they were expecting the hunters to come save one of them. Instead the wolves came and killed them before true reconciliation.