I know DHCP supposed to provide ip to machines, but need to know how they handle when things dont go well.

ie
1) do DHCP communicate with each other ? assuming many DHCP in the network with the same setting, will they fight or work together ?
2) multiple DHCP in a network, what will happen when a new machine come in ? get ip from a random DHCP ? any idea which 1 get priority?
3) if a machine already used a fixed ip, but that fixed ip is in dynamic ip address range, will that IP get offered ?