I would not do that....the brackets are strong but a 20' beam is allot. I used middle brackets for a 16x16 carport, 8' 4x4 length, 16' sandwich 2x4s on front, middle and rear and it seems to be holding up .
Yes, the brackets come with installation hardware. According to the product description, it includes 48 drill tail screws and a comprehensive installation guide.
Yes, the brackets are compatible with shade sails. The product description states it comes with sunshade sail attachment holes that allow you to block sunlight and protect belongings from moisture and damage.