How does Booking.com work when you book for a large group?

I want to organize a big family trip that would include about 15 people altogether. We've been planning it for a while, and we already set the time and destination. We just haven't picked our travel agency yet. Somebody recommended Booking.com to me, which is why I'm interested in learning more about it.

Can it handle larger groups of people, or should we opt for local agents instead? Also, are bookings for a group of people cheaper (as in bundle discounts)?