Pip: Mr. Peepers, Peeper Dog, Peeper Beeper, Pipper Dog, Pip Dip, Pipperoni Pizza, Good Pip Lollipup, Pippers, and various combinations of the above.
Maisy: Maisy Bee, Maisy Bee-hind, Maisy Mayhem, Maisers, Maiser Beam, Houndy, Silly Pants, Pretty Pants...
Squash: Squashes, Squashies, Squish Squash, Squashy Washy, Mr. Squashies, Puppy Pants, Squishy Pants, Polar Bear, White Dog, Pink Dog, OH GOD NO WHYYYYY WOULD YOU DO THAT... wait, that last one just FEELS like a nickname because I say it so much.