Of course, the Vampire himself is considered a Sleepwalker for banner bearer and could carry the spell himself.

As a practical matter, a starting mage with an Augment the Mind rote can grant + 3 Intelligence & + 2 Resolve for 5 individuals Indefinitely.

It would be Gnosis 1 + Mind 3 + 2 High Speech + 4 Rote Skill + 5 Ritual + 3 Willpower = 18 - 10 (Indefinite) - 4 (Extra Potency for Resolve) = 4 dice.

It's a 15 hour ritual with a 75% chance of success.

It requires +1 Reach to enhance two stats + 1 Reach for Indefinite + 1 Reach for Advanced...