Obviously, if any of the contacts weld together, that's it. I know that there are problems paralleling diodes but I don't know if, and don't believe, the situation is the same for relays. If you don'
Not quite on the voltage, I think. Whether open or closed wouldn't the first in the series have full voltage to ground or to the coil ? Onl;y if they were indeed mechanically and electrically daisy c