"She always puts others first," the singer tells PEOPLE

Credit: Mei Tao

This Mother’s Day is bittersweet for Colbie Caillat and her tight knit family.

With the recent death of her grandmother, Beverly Jean Leineke Andert, the singer is celebrating all the women in her family this weekend, including her mom Diane Caillat and her sister Morgan Caillat Stockmeir, who welcomed a baby several weeks ago.

“My mother is the most selfless woman,” Colbie, 29, tells PEOPLE. “She always puts others first. She inspires me to be myself, and accept who I am, appreciate how I look naturally, like she has always done with herself.”

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Living just a few minutes away from her parents (Morgan also lives around the corner), “our family has always been close,” says Colbie. “[My mom] has made our family’s lives so fun and full of love.”

Seeing each other “three to four times” a week, mom and her two girls love “just cruising with all our dogs,” says Diane, a former model turned entrepreneur. “[We have] six of them between us!”

Colbie’s parents often travel with her on tour (“She wears my tour shirts, which I get embarrassed about,” says the star, laughing), but even now that she’s playing to huge crowds, Colbie “hasn’t changed a bit under the circumstances,” Diane explains. “She’s only just gotten better and better.”

For more on the Caillats, pick up the May 11 issue of PEOPLE