Archaic honorific second-person plural pronoun. Used in historical or classical contexts to address multiple people respectfully. In modern Japanese, あなたがた or 皆様 are used instead.
御前方には、このたびのご尽力に深く感謝申し上げます。
To all of you, I express my deep gratitude for your efforts on this occasion.
Singular 'you', originally honorific but now casual or intimate. 御前方 is its archaic plural form.
Compound of 御前 (おまえ, 'you', originally honorific) + 方 (がた, pluralizing suffix). The exact historical derivation is uncertain, but it follows a pattern of forming plural pronouns with 方.