Much more usable diagram. 
joatmon13:
4) My understanding of a bridge rectifier is to switch ac to dc. So would it not in fact stop the system from reversing polarity to the actuator when required?
It is just a convenient way of attaching to each actuator connection, a pair of diodes which prevent the voltage either exceeding the supply voltage or going negative to the ground (12 V negative). Under normal operation, that clearly cannot happen, the diodes merely limit impulses out of the range of the supply voltage as the relay contacts change over. Two wires, two diodes each, a bridge has them all.
joatmon13:
5) Can anyone explain why the 12v output from the relays would switch to a negative value, less than required (-0.7 to -8v). Is this because of the long leads between the relays and the actuator? (2.5meters).
No. If it is wired correctly and you were measuring correctly, then other than switching transients - which you would need a scope to observe - no part of the circuit generates negative voltages.