Anna Kepner’s grandparents are shutting down any talk she was scared of her stepbrother — the teen reportedly under investigation in her cruise-ship death — making it clear they have faith in his innocence.

In an ABC News sit-down interview, Barbara and Jeffrey Kepner said 18-year-old Anna and her 16-year-old stepbrother were “two peas in a pod,” and cared for each other “in the right way” — a far cry from what Joshua Tew, Anna’s first love, claimed … saying her other brother told him about a nasty blowout the pair allegedly had inside the cabin they were all sharing.

The grandparents say authorities told them the stepbrother is considered a suspect in the case. They admit they’ve got no clue what actually went down inside that cabin — they’re waiting on answers just like everyone else — but pointing the finger at the stepbrother? They’re nowhere near ready to go there.

The family says this cruise was meant to kick off a new tradition — a big, blended-family getaway — and they vividly remember the last night they saw Anna. Her braces were bugging her at dinner, but she powered through, stayed for the fun … then headed back to her room.

As you know, the cheerleader’s body was found in that shared cabin on Nov. 8, reportedly wrapped in a blanket and tucked under a bed … as we reported, she died from asphyxiation reportedly caused by a “bar hold,” basically someone’s arm pressed across her neck. She’s not believed to have been sexually assaulted.