Rebecca,
Your leveling system does have a separate fluid reservoir from the one that you referred to that powers the power steering, and it is connected to the leveling system pump. You can locate the pump by having someone operate the leveling system from inside the coach while you lessen form outside the coach. The pump noise will lead you to it's location. However, I do not think that low fluid level is your problem because raising or lowering the jacks is only transferring fluid from one side of the jack piston to the other and not depleting fluid from the reservoir, but it doesn't hurt to check.
Your leveling system problem sounds like a control module or solenoid problem instead of a pump problem, because very little pressure is required to raise the jacks. If you can not determine the problem, you can just loosen both hydraulic hoses at each of the nonfunctioning jacks, but this can be dangerous as that will lower the coach as the jacks retract, so safety supports are needed. Loosening the hoses and tightening them after the jacks are fully refracted will make the coach drivable, but you will not have a leveling system until it is repaired.
As for replacing you house batteries because they are 3 years old, that is a bad idea. Your house batteries should last from 5 to 8 years will reasonable maintenance. Also, there is almost no chance that batteries are causing your problem if you are plugged into shore power with the house batteries being charged by the inverter and the chassis batteries being able to start the engine.
Gerald