Hi,
Well they are brigaded together in all sources I've seen. The brigade is the single largest brigade in either the Army of Portugal or the Army of the North at Fuentes de Onoro, the majority of the other light cavalry brigades are much smaller as are the two brigades of dragoons (individually). Oman lists
Lancers 30 340
Chasseurs 13 222
Mamelukes 10 69
Grenadiers à cheval 12 185
65 offices and 816 other ranks
Reading up on the reorganisation Massena undertook prior to Fuentes de Onoro, he had reduced most if not all of his cavalry to two squadrons, and some only one, sending the cadres back to Bayonne for remounts.
Taking between 100 to 120 as being the lowest possible number of officers and other ranks for a unit to continue to function as a squadron, IMO the brigade might comprise eight small squadrons or possibly four or five large squadrons (with a small unit of mamelukes attached?) Think I'd go for eight smaller squadrons
Bessieres has two brigades of cavalry Lepic and Wathier, for Lepic's appointment to the command of the guard cavalry in Spain see:
Correspondance inédite de Napolón Ier: conservée aux Archives de la guerre
by Napoleon, Ernest Picard, Louis Tuetey - H. Charles-Lavauzelle p 530
http://books.google.com/books?q=lepic&id=bbQ6ADXNXlMC&vid=LCCN13023905&dq=lepic+berg&hl=en&ie=UTF-8&pgis=1
Ant