Lawson was noticeably wearing a baby blue T-shirt that read, "soon to be a Big Brother."
"We're having a baby but we don't know what we're having yet!" Jeff announced. "Baby No. 2 is on the way!"
The crew of Jeff's YouTube show then joined the family onstage to celebrate with a cake and balloons.
Jordan, 31, also shared a picture of herself Monday on Instagram 16 weeks into her pregnancy and revealed the child is due in September.
"This time around I feel like my stomach popped sooner than it did with Lawson. My doctor told me it would & said it's normal. Being nauseous is gone, but I'm still in that tired phase. Patiently waiting, & hoping it goes away soon since I'm in my 2nd trimester," Jordan captioned the mirror selfie, which showed her in blue and white pajamas.
"I never had breakouts or headaches when I was pregnant with Lawson but this time I'm battling the never ending pimples/boils on my chin... The headaches get to me because they never go away!! Sometimes it last all day & it doesn't help when you have a screaming toddler around."
Jordan continued in her post, "Besides that, everything else is going good so far! I go to the doctor Wednesday & find out what we are having!! So excited! This whole time I was thinking boy, & now I'm thinking girl. We will see...!!!"
Jeff and Jordan met on Big Brother's eleventh season back in 2009.
Jordan was crowned the winner of BB11, but Jeff at least walked away with the honor and title of "America's Favorite Houseguest." The couple later returned to compete on Season 13 and then got engaged during a 2014 episode of the show's sixteenth edition.
Jeff and Jordan were planning to marry in September 2016; however, the situation changed once Jordan found out she was pregnant in February of that year.