Then they will eat a lot of kibble.
If they're all male, you can go with Huey, Dewey and Louie. Or Groucho, Harpo and Chico. Or Moe, Larry and Curly. Or Rob, Chip and Ernie (anyone who used to watch the old "My Three Sons" TV show will get that one. The others, in order, are: Donald Duck's 3 nephews, the Marx Brothers and the 3 Stooges).
For three females, hmm, Piper, Paige and Phoebe (the sisters on the "Charmed" TV show)? Masha, Olga and Irina (the Three Sisters in Chekhov's play)? Meg, Jo and Beth (the three oldest sisters in "Little Women". The other one is Amy, in case you wanted to swap)? Rachel, Monica and Phoebe (the 3 women on "Friends")?
2 boys and a girl: Peter, Paul and Mary (folk singing group from the '60s). Or Sam, Dave and Maddie (the love triangle from the old "Moonlighting" TV show). Daisy, Bo and Luke (the Dukes of Hazzard).
2 girls and a boy: Peppermint Patty, Marcie and Charlie Brown (from the Peanuts cartoon). Or Lisa, Maggie and Bart (the kids on the Simpsons).