Never have two basses up.
Never.
NEVER!
this
A, it sounds shit
B, if your playing one track correctly it should be on near maximum output (i.e. near the red line) and if you play another track at the correct gain, it will distort.
this isn't to say you should just have 1 bass on full and the other on min. although this can work for a lot of mixes but isn't always best.
but yeah, it all depends on the tracks ur mixing and what sound elements are involved.
having the bass turned down on one track will make the mid and treble stick out more, so just by subtracting some bass you may need to subtract elsewhere too, on the same track or on the other one.
for treble its very rare i will have both tracks on maximum, this also sounds poor imo, too much treble will clash, sound tinny, and depending on the tracks you will most likely have hi hats all over the place and will sound messy. also when ur beat matching goes slightly off this is where you will hear it, lower the treble and the lil slips will be less noticeable.
best advise i can give you is..
find a mix with 2 tunes you like, with a nice blend using the intro and also the bass lines together too.
record it several times using different methods of eq each time, listen back and see which you prefer. i find mixes can sometimes sound different recorded to how they do live.
if you have a mix you like and i have both of the tunes, i will upload a snippet of audio and note what positions i would personally eq them at. I'm not clamming to be an expert on the subject coz I'm far from it, my ears are shot to bits, but if i can help i will try.
eq's can sound different from mixer to mixer so its not always gonna be the same.