If you follow the symbolism alone... 💧

I think the body in the water will be one of the Ratliffs, and more specifically, possibly one of the brothers.

The 'Saxons' were coastal raiders who attacked the Roman Empire using boats.
'Lochlan' means "land of the lakes".

The tsunami theme and nightmarish dream. We see other characters in pools, but never natural bodies of water. The constant water elements lurking in the Ratliff scenes and cinematography, their blue wardrobes with alligators and fish and preppy naval influence, the boys' names laced with heavy aquatic symbolism – to me, this all seems to be foreshadowing a very watery fate for one of the Ratliffs.

Also of interest:

Saxon = "dagger/sword" (German origin) – Violence and/or death.
Ratliff = "red bank/cliff/steep slope" (British origin) – Imminent danger.
Victoria = "victory" (Latin) – Does Victoria have anything to do with her husband's downfall?
Timothy = "honoring God" (Greek origin) – A befallen man seeking salvation.
Piper = "pipe/flute player" (British origin) – As the daughter and black sheep of the family, this name really sets her apart from her brothers, and hints at her more expressive and unique nature.