Should be okay to mix them up.
But names do have significance and the reader might wonder why certain characters are named differently.
Although it's a bit different because you have pictures to match the characters, reading a name can make someone visualize things differently. Someone named Fiona would be differently perceived as, say, Roscoe, Al, or Gwendolyn, etc.
I'm probably over-thinking it, but with such a short word count, I wouldn't take anything - even names - for granted. I don't have a pet but it might be like naming one? Or naming stuffed animals when you were a kid. Names need to fit the character.
-
Winnie the Pooh might be a good example of this:
In the series about Franklin, the turtle, he is Franklin and everyone else is Bear or Beaver. In Winnie the Pooh, there are Winnie and Eeyore, but Piglet, Rabbit, Owl, Tigger, Kanga, and Roo.
The Winnie part of Winnie the Pooh was named after a bear from Winnipeg and the Pooh part is sorta explained here:
But his arms were so stiff ... they stayed up straight in the air for more than a week, and whenever a fly came and settled on his nose he had to blow it off. And I think - but I am not sure - that that is why he is always called Pooh.
And, interestingly, Eeyore's name, I think, comes from the noise donkeys make eeeee-ooorrr.