Controlling a double solenoid valve?
You need to know how the solenoid valve operates. Some remain in position with no current to either coil. Others are designed to return to a center position when coil voltage is removed. Still others require sustained voltage to a coil to keep them from drifting to an undetermined position. NONE of the solenoid valves I have looked at will operate properly with voltage applied to both coils, so your PLC program will need interlocks to prevent this condition. Use of Set Reset coils is not really necessary unless you have other considerations which would make their use preferable. Sorry not to be more helpful, but in this case, knowing the application and hardware is essential..
It depends on the valve construction. If it's a 2-way valve you may need to hold it open by keeping the output energized until you want to shut it off. In this case I would use Set and Reset instructions. If it's a 3-way valve with a block center that hold pressure on that side of the cylinder, a simple OTE instruction will work fine.
Cheaper and more reliable to use simple coils...You probably need to add a large transistor between PLC and coil, with a bypass diode, unless your PLC output can sink a LOT of current.
You may want to check with the company that manufactured the valve - that would be your most likely source.