The word subisteis is the preterite form of subir in the second person plural.
See the full subir conjugation

subir

Y, cuando subisteis al Cadillac, ¿fue la primera vez que viste a Chen?
So, when you guys got to the Cadillac, that was the first time you saw Chen?
Lo hemos logrado por un libro de una biblioteca que había en las fotos que subisteis.
Got it off of a library book from the photos you guys uploaded.
Subisteis hasta el nacimiento del Nilo.
You went up to the source of the Nile.
Ya, así que la metisteis en tu coche, la subisteis aquí, ¿y en ningún momento os pareció que pesaba demasiado?
Yeah, so, you put it in your car, carried it up here, and not once did it seem a little heavy?
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