The first step is to determine which preposition properly complements the past participle of the verb used adjectivally.
We are surrounded by friends and family.
We are grateful to those who surround us.
We are grateful to those by whom we are surrounded.
We do not say:
We are surrounded to friends and family. ungrammatical
We are surrounded in friends and family. ungrammatical, or marginal
I noted that surrounded in is marginal because surrounded in is permissible when that which surrounds is not made up of discrete individuals with volition and acting in concert but is an enveloping thing:
It is surrounded in mystery.
Hearing surrounded in used in that way, some speakers might say:
I was surrounded in people at the train station.
and mean not that the people encircled him or her, but that it was crowded and he or she was in the midst of the crowd. There were people on all sides. Surrounded in refers to that which surrounds as something inchoate, a mob or crowd in this instance, rather than individuals.