The rule in traditional grammar is that the form should be "to my brother and me" because you use 'me' after a preposition (to).
To decide whether to use "me" or "I" in expressions that use 'and' drop everything but I/me and it will be clear.
They talked to (my brother and) me.
(Surely you wouldn't say: They talked to I.)
(My brother and) I went to the movies.
But usage is changing now. What seems to be happening is a switch from the old rule (as detailed above) to a new rule:
use 'me' before 'and'
use 'I' after 'and'.
Actual usage for many people is a combination of the old rule and the new rule.
Someone is talking to you and me. (I'm nopw not so sure this one is correct but it probably should be)
yes, subject of an adjective.
1. Adjectives don't have subjects in English.
2. There is no adjective in the sentence "Someone is talking to you and me."