MARLBOROUGH, MASS. — Advocates, a nonprofit organization that supports people with behavioral health disorders, disabilities and brain injuries, has signed a 95,182-square-foot office lease in the western Boston suburb of Marlborough. The deal brings the 160,649-square-foot building at 251 Locke St. to full occupancy. Alison Powers and Robert Walles of JLL represented the landlord, Related Beal, in the lease negotiations. Jon Pezzoni of Avison Y…