David Foster's daughters hate how "hot" their stepmom is

Erin said: "Our biggest issue with Katharine is how hot she is. Her body is insane. When she comes over for family Sundays, I'm like, 'Do not get in a bikini.' My husband's always like, 'Kat, get in the pool!' And I'm like, 'Simon!' ... Interestingly, the age difference has played a role in a positive way. Our dad comes from a generation where women are more passive. He is also passive about his feelings. Kat has really pushed him to open up. We could get into a fight, and then Kat's like, 'No, you have to pick up the phone, call your daughter back.' She's a facilitator, which is really important. She pushes him to be more emotional and more vulnerable."

And Erin insists her and her siblings are not in "competition" with the singer, and they only want the best for their dad.

Speaking of their relationship, she added to People magazine: "We've been through a lot with each other, and we've arrived at a place in our lives where we're all happily in our own relationships. We want our dad to be happy in his relationship. We are not dating our dad so we are not competitive with the woman who comes into his life. We want him to be happy, and it doesn't matter if she's our age or if she's his age because we just want him to be with a good person. And the truth is, ironically, it's much easier for us to get along with someone who's our age because she's similar to us. She's someone who we would be friends with."