Anna Kepner and Her 16-Year-Old Stepbrother Were Like '2 Peas in a Pod,' According to Grandmother By Samira Asma-Sadeque 42

The grandparents of Anna Kepner, the 18-year-old cheerleader found dead aboard a cruise while on a family holiday, say that the teen was very close with her 16-year-old stepbrother, who is now a possible suspect in the case.

The 16-year-old boy has not been named a suspect by the FBI, which previously confirmed to PEOPLE it is investigating the case.

Kepner, of Titusville, Fla., was found dead on the Carnival Horizon cruise ship on Nov. 8 by a member of the ship’s housekeeping staff.

No suspects have been publicly named.

However, in court filings related to a custody dispute, Kepner’s stepmother Shauntel Hudson claimed that investigators say her 16-year-old son — Kepner’s stepbrother — may be subject to a criminal case following the teen’s death. (Shauntel’s last name is listed as “Kepner” in several media reports, but court documents identify her as Shauntel Hudson.)

Shauntel Hudson’s ex-husband — who is the 16-year-old’s biological father — also said in a petition filed with Brevard County that the teen is a “suspect in the death of the step child during the cruise,” according to the filing obtained by PEOPLE.

The attention on the stepbrother, however, appears to have caught the Kepner family by surprise.

Kepner’s grandmother, Barbara Kepner, told ABC News in an exclusive interview that the family was close-knit — especially Anna and her 16-year-old stepbrother.

“They were just like brother and sister,” Barbara said, adding that they were “two peas in a pod,”

“I know that those two kids cared about each other in the right way,” Barbara said, while declining to comment about the scrutiny on Anna’s stepbrother.

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Anna is being remembered for being a “thoughtful” and “nurturing” member of the family who took special care of her siblings, “taking them to the park, Halloween Horror Nights, or just out for fun,” her loved ones said in an online obituary.

“She had a big, beautiful heart, often sending random ‘I love you’ messages or little gestures that made someone’s day,” read part of the obituary.

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Much remains unknown about the circumstances surrounding Anna’s death and the ensuing investigation as authorities remain tight-lipped about the case.

While a cause and manner of death have not been officially announced for Anna, sources close to the investigation previously told ABC News that she died from asphyxiation from a “bar hold” — or an arm held across the neck.