Seperating depends entirely on your flock and momma. Cochins generally are great mum's though. What ever you decide to do make sure to keep a close eye out when hatch time approaches. I had muscovy eggs under one of my chickens she's hatched chicks before so I didn't expect a problem but came...
Definitely drakes. The safest thing would be to house separate or re-home. I have had drakes with chickens that never showed an interest in mating the chickens but I've also had a drake who would seek out the chickens obsessively to mate. Also the drakes could be fine this year then next year...
My two older girls atleast 3 years look similar feather wise at the end of the season, I believe neither were around water to bath in prior to me getting them so they very very very rarely get in the water but will stand at the side of the water and flick water onto themselves with their heads...
Egg looks alright to me, definitely the liquid you saw could have been the chick moving, if the air cell gets alittle wonky it can look very strange. Unless your positive an egg is dead, like no question what so ever leave it incubating. I've had a couple eggs that I was convinced were...
Following the other around and nibbling on each other is normal, one trying to cuddle with the other can also look like chasing, but if it's truly chasing, trying to corner it and pecking hard not just nudging/nibbling that could be a problem. Are they still in the incubator? If so the older one...
Bantam hens and standard roo here, we never have a problem and one of my hens is an old english she's tiny her eggs are small and odd shaped occasionally I have to assist her eggs but I think that's due to the shape not the size.
The chick knocking the eggs around shouldn't really be an issue if they are all about ready to hatch. Same thing happens under a momma hen. And the peeps encourage the others to hatch. But if your wanting a nursery pick up a cheaper incubator dosnt need to be fancy to throw the fresh hatched...
Probably be fine, if it were me I'd just watch closely and snatch shells as they hatch and pull chicks as soon as is reasonable. Once a couple hatch and get moved out they should be fine.