It's often assumed that twin siblings share just about everything—and in the case of actress Brittany Daniel and her twin sister, Cynthia, this statement has been true to their relationship throughout their entire lives.

Best known for playing twins Jessica and Elizabeth Wakefield on the hit UPN show, Sweet Valley High (raise your hand if you owned all the books back in the day), the Daniel twins have a bond deeper than most.

After Sweet Valley High went off the air, Brittany Daniel continued acting, while Cynthia married Yellowstone's Cole Hauser and had three kids of her own.

"I always thought I'd be the first to get married and start a family," Brittany tells PEOPLE in a new interview. "But I was serious about my career, and I was having a good time."

In 2011, Brittany was diagnosed with stage IV non-Hodgkin's lymphoma. After going through six months of chemotherapy, she was ready to find a partner and start a family.

"I remember thinking that I had a new lease on life," she says. "I was ready to find a partner and have a child."

Because of her battle with cancer, conceiving children on her own presented its own set of challenges. Due to the intense chemo she endured, her egg reserves had diminished. When she talked about it with Cynthia, her twin sister didn't hesitate to donate her own eggs.

"I saw it as such a simple gift I could give to her," Cynthia says. "I know Brittany would do it in a split second for me. And we've always shared everything, so why not this?"

Brittany married broker associate Adam Touni a few months later, in 2017. The couple underwent three rounds of in vitro fertilization using Cynthia's eggs, unsuccessfully. But that all turned around in the fall of 2021, when she and Touni welcomed their daughter Hope after finding a surrogate to carry their child.

Both mom and dad were in the room when their daughter was born.

"I just let out this primal cry," recalls Brittany of meeting her daughter. "The entire room was bawling because they just all knew what we had been through."

Aunt Cynthia got to meet her niece in December (following Covid safety protocol and self-quarantine).

"I wasn't sure how I was going to feel at first, what emotions would come up," she says. "But I just felt like the aunt. And that is really special."

What a beautiful gift between sisters. As a sister myself, I know I wouldn't hesitate to help mine conceive or carry a child if that was something she wanted and needed. I help in any way I could—without question.

As for Brittany, she's forever grateful to her twin for giving her the gift of motherhood:

"My sister made my dreams come true."