The black one looks like he could be a silkie cross, i say that because of - His crest, his facial expression, and he's not exactly a large bird, him being red faced doesn't matter. He has a funky rose comb going on so i would think he's crossed with a rose combed breed i couldn't guess which, he may even be a three-way cross.
The Silver duckwing, i would guess a old english game bantam over production breed... Look for heavy breeds with blue legs. Again though it's really hard to tell with crosses, because if coming from someone who just let their birds run loose they can be three, four, or five way crosses even between crosses and not show much a resemblance to their heritage.
Depends, if you just want a few pretty birds to free range or own. I don't see why not- they are free. If used for breeding purposes i wouldn't get them. Remember to quarantine if you do get them...
The first guy looks like a Cochin X Silkie. Unless that little speed-bump on his head is not a crest, but the result of some lost and growing feathers that he's getting (it looks like he's molting, 'tis the season). And he's sporting a fine 'coral comb' (rosecomb).
I'm not even going to bother with the second one. If you'd like some roos and they're nice, friendly, healthy looking in person, go ahead.