The "shuttle valves" are a part of the main pump/modulator. They are a common problem on the Wabco system. Mine failed so I replaced it with a 2nd hand modulator - it failed with the same problem after a couple of years - I once again replaced with another 2nd hand modulator and this one has been running fine for a number of years now. I have seen just the shuttle valve bits advertised for repairing the modulator when this error occurs but I've never tried them. The same unit is used in the Discovery2 and there is a messy fix described for that which presumably would work for Freelander.
Dunno what the open relay message is about.
The sensor message is presumably what it says.
These codes have presumably been raised at different times - you won't know what raised the fault yesterday presumably.
Sensors can be bought and shipped easily. A replacement pump/modulator might be difficult there if there aren't many Freelanders being scrapped - you need a unit from a 1997-2000 car, from 2000 on they were different Teves units.