The sisters and style-setters shared their best dressing "dos" for wedding guests at the launch of Conair's The Knot Dr. Brush


Erin and Sara Foster are gearing up for a big family wedding — their dad, musician David Foster, is set to wed American Idol alum Katharine McPhee this summer — and the hilarious sisters are prepping with heat-proof hair and makeup, plus an expertly styled outfit (in any color but white, of course).

“For summer makeup, I switch from powder shadows to cream shadows and powder bronzer to cream bronzer,” Erin told PEOPLE at Wednesday’s “Knot-A-Real-Wedding” event to launch Conair’s The Knot Dr. Brush, a detangling tool that features an attached protective case. “I think you’ve got to dewy your face up. Erase the sweat and turn it into dew. That’s the way to go.”

Erin Foster and Sara Foster
Credit: Craig Barritt/Getty
Erin Foster and Sara Foster
Sara Foster, Dj Quintero, Erin Foster and Nina Agdal celebrate “Knot-A-Real-Wedding” in honor of Conair’s The Knot Dr. Detangling Brush
| Credit: Craig Barritt/Getty

The Bumble founders, who officiated the Conair faux-wedding, suggest embracing the inevitable humidity at any summer ceremony. Sara says, “Humidity is amazing for your skin. It might not be great for the hair but it’s great for the skin because it’s like moisture.”

As for wedding guest fashion, the sisters have some conflicting opinions. Sara (who admits her sister is actually the hair and makeup connoisseur but says her closet is way more raid-worthy) tells PEOPLE a cream look could be chic. While Erin is adamantly opposed and says you should never wear any shade of white to a wedding.

Erin Foster and Sara Foster
Nina Agdal, Erin Foster and Sara Foster celebrate “Knot-A-Real-Wedding”

“Okay, first and foremost, don’t wear a wedding dress to a wedding,” Erin says. “Second, don’t wear white. Don’t be too sexy. But if you’re single, be a little sexy because there are dudes at weddings and there are hot girls too.”

One fashion tip they can agree on? Dolce & Gabbana floral prints are a go-to for summer nuptials.

2019 Billboard Music Awards - Arrivals
Erin and Sara Foster
| Credit: Frazer Harrison/Getty

Last year, the stylish sisters shared a few other favorites with PEOPLE, including Leatherology bags and goop bodysuits for Sara, and Frame corduroy pants and La Ligne sweaters for Erin.

“If I see one cloud in the sky I put a sweater on,” Erin said. “La Ligne always has comfortable, creative, and flattering options.”

Sara added: “La Ligne is a newer label out of New York that I discovered a couple years ago. Between their sweaters and dresses, everything they do is unique and comfortable. I’m obsessed with their patterns and colors.”