http://www.planetcatfish.comI think the first ones are some type of Synodontis. Have a browse
here and see if you can recognise them. Though they do look a bit like
featherfins. You can see the fish properly to compare to photos on those sites. If they are featherfins, the last link gives their size as "12 inches, though 6 to 8 inches is more common in aquaria" needing a 4 ft/120cm long tank; and "should not be kept with any fish so small as to be considered food" So yes, they could be responsible for your fish losses, especially if they were small fish.
The bottom pic is definitely a plec, and I have a bad feeling it is a common plec ie a tankbuster. It looks very like the middle pic
here. You could ID it better if you go to planet catfish and search through all the L numbers in the cat-e-log. But you'd need to set aside a whole day as there are so many of them
If it is a common plec, it needs a huge tank. The very conservative fish profiles on here say a minimum of 150cm long.