On Thursday, Jason shared a selfie with his wife of the two on a boat on crystal blue water, with rock formations the background and a cloudless sky.
"I have to say, me and this beautiful mama have seen a lot of places over the years but Cabo San Lucas is AMAZING!!!" he wrote. "Thanks to @diamondresorts for having us this weekend for my lil sisters wedding. #firstclass."
In another shot on his Instagram Story, Jason posed in a tropical-print shirt, a pair of teal shorts and loafers, holding a drink and dubbing himself "Mexican [as f—]!"
Brittany is also documenting the trip on her own page, kicking things off with a hilarious photo of herself and her husband giving the camera their best duck faces before heading to the beach. Brittany wore a neon yellow and navy blue bikini with a colored headwrap while Jason opted for a blue Under Armour shirt and a pair of swim trunks, completing the look with an appropriately branded baseball cap.
"Give em that epic duck face, babe," Brittany cracked in her caption.
During their excursion, the couple headed to Lovers' Beach, with Brittany writing that they felt right at home alongside a photo of the duo sharing a smooch on the water.
"Just fitting right in at Lovers Beach," she captioned the snap.
The 32-year-old also gave her followers a look at her and Jason's gorgeous accommodations for the trip, which include a bedroom with floor-to-ceiling glass windows that offer a stunning view of the beach as well as a bathtub literally right next to the bed.
Williams is marrying singer and radio personality Chuck Wicks, and the two couples can often be spotted hanging out together on social media.
"I've known Jason for a long time, but yeah, I was a little tentative at first about dating his sister because what if it didn't work out?" Wicks told PEOPLE. "It was a little nerve-racking. I didn't want to screw it up."
He didn't, and after dating for around one year, Wicks popped the question earlier this month during a romantic vacation in Canada. When he marries Williams this weekend, Wicks and Jason will officially be family.
"I love everything about our relationship," Wicks gushed over his soon-to-be wife. "It almost feels like a Disney movie. It's hard to believe this is all happening."
Photo Credit: Instagram / @jasonaldean