Thanks for pointing it out. I missed that paragraph repeatedly.
MA Sweeps and Brawling are both pretty self-explanatory.
For Combat styles that might be applicable here are the ones I would consider from HARP and ML:
Mounted Combat
Weapon & Shield
There may be others introduced in Harpers Bazaar issues, the Cyradon product or The Guild Companion articles.
For multiple people attacking at once I would also give additional bonuses for facing. One individual is assumed frontal. Two are both assumed flanking. Three are 1 frontal and 2 flanking. Four are 1 frontal, 2 flanking, 1 rear....
If you look at the July issue of The Guild Companion, I wrote an article about creating Training Packages - specifically for Thieves World. At the end there are some talents that I created including one which handles well-coordinated joint attacks. If used in your game you could also apply that in this situation.