Regarding solenoid valve
Each solenoid requires 2 A.
Your power supply is rated for 2 A.
You can power one solenoid valve at a time.
You would need a 4 A supply to power both of your solenoids.
The diodes won't make an extra 2 A appear out of nowhere.




simulate this circuit &ndash; Schematic created using CircuitLab
Figure 1. Snubber diodes. You can still only power one 2 A solenoid from a 2 A supply.
The diodes should be connected as shown. Normally they don't conduct but when the relay contacts open they provide a decay path for the current and protect the relay contacts from arcing damage.



simulate this circuit
Figure 2. As suggested by @SpehroPefhany, this arrangement ensures that only one solenoid can be energised at a time with SV1 getting precedence.