These two boxtrolls are Fish's buddies. However, when Fish first brings in Arthur, they come across as a little judgmental. They make "spluttering noises" (5.14) that are interpreted as mocking Fish for befriending a human so quickly. When Willbury berates them for sn*****ing at Fish, though, their faces turn "bright red" (5.15), so we're going to go ahead and say no harm, no foul when it comes to these two.
It seems like they're still good buddies with Fish, though. When Fish's suggestion for an underground hole to get Arthur home turns out to be sealed up, "Shoe and Egg were comforting Fish" (8.7). They all like junk food, which Willbury takes them to task for, causing them to "look rather guilty" (11.77). In other words, they might make spluttering sounds, but they've still got feelings just like everybody else.