Don't see any mounting screws and/or nuts in the photo. Are they included with the stays?

Yes there is a hardware bag with Allen screws in it

what is the weight of these without packaging? also are they steel?

These weigh in at 195 grams each, and are steel!

are both stays the same length? I was thinking of purchasing one set to use for the back fender for 2 bikes, the front fender is fine without the stay

Mine were both the same length, I have a 1.95 MTB tire on my front and I had to rig up an extension. Back had plenty of room, so you should be set to go.

Package didn't come with nuts and the screws do not fit in the holes they're supposed to go through. Has anyone else had this problem?

Mine were included with the fender struts. One did require excessive pressure to screw into the bike frame mount. But. I believe that was caused by an overabundance of paint in the mounts threads, not the bolt.