gauge install help plz

You can connect all the grounds for the gauges together (the two lighting grounds and both gauge grounds). Then run one wire from where you connected all 4 wires together, to a solid ground. Any bolt on shiny metal should suffice (where you're gauges are being mounted will determine this). No need to run the grounds to the negative battery terminal as some instructions indicate.

You will want to find a 12 volt source that's hot only with the key turned on. Again, location determines this most of the time. A source from the fusebox is always easy.

You got the positive wire for the lightning nailed. If your gauges are near the radio and your radio harness has an illumination wire that works, you could tap into that (or at the HVAC lighting wiring). Fuse 13 is real easy though if that's preferred.

The sending unit for oil pressure is above your oil filter. The stocker screws into a hex tube lookin deal, and the stock sender looks like a bell.
You can use a tee for the OP senders if you like.

For the water temp gauge, I'd put the new guage's sender in the stock location. Then move the stock sender somewhere else (rear of the intake manifold, into a tapped T-stat housing, etc). You want your most accurate gauge to read from the stock location. And you should not use a tee for temp guages (hence jumping through those hoops).

Good luck and enjoy!