would i put ser, estar, somos, or estamos in front of sentandonos en el arbol

Thank you for using the Jiskha Homework Help Forum. When you see a gerund (the -ndo form) it is usually a form of estar in front of it.

We are sitting in the tree:
Nosotros/nosotras estamos sentándonos en el árbol.

Sra

P.S. This tense is called the Present Progressive meaning estar = -ndo. You also have the choice with a gerund of putting the reflexive pronoun (nos) in front of the conjugated verb = Nosotros/nosotras nos estamos sentando en el árbol. That way you don't have to worry about accent marks!