for the Tee, two options. one of which you already listed. i would take all your fittings with you, into the store, and match stuff up. i had to put a 1.5" extension pipe on the 'hex' tube (that the oem oil sender screws into), so that my two electrical senders would have clearance.
option two is to hit the parts store. with the gauges they sell, they sell a Tee fitting. it is normally all 1/8" female fittings in the Tee. might need to get some 1/8 to 1/4 fittings at the home store - like i said, piece it all together.
good luck.