First of all depending how your valves are assembled, youd have to tap into or branch off of the assembly AFTER your fill valve.
Lets say you used a brass T.. instead of using reducers and branching off, possibly slowing down your speed.. try to find someone to drill and tap the brass T for a 1/8" NPT fitting. you can even pick up the tap at lowes for like $5.
Then you basically run small line, 1/8" from each of those Ts to each of your gauges fittings.
Here's an example of the fittings added to the Ts I use:
Hope that helps some, also.. if your gauge is anything like the ones I usually use.. itll be a pain in the ass wrapping teflon tape.. I found it easier to use liquid teflon for those small fittings on the back of the gauges. the mounting screws/light fixtures got in my way. let me know if you need help with getting the line/fittings.
Good luck man