So, whether then it was I or they, this is what we preach and this is what you believed [what you adhered to, trusted in, and relied on].
Therefore whether it were I or they, so we preach, and so ye believed.
Whether then it be I or they, so we preach, and so ye believed.
So then, whether you heard the message from me or them, this is what we preach and this is what you have believed.
For whether it is I or they: so we preach, and so you have believed.