With a powered kemper and a 4x12 stack, you should not have volume issues. You did not describe how much power your bandmate is delivering. What about his EQ settings? Mid scooped? Treble boosting? Do you have the same volume as him or is this just an EQ cutting issue? Are you getting sucked by your reverb or too much gain compression?
A 2 guitar band where players harmonize and give a musical outcome is a lot of fun. Talk to your guitar mate, experiment together, for your solos dial in more high end than you would playing by yourself, use less lows/bass, less gain helps, too. If the other guitar díals the same EQ approach as you do during your solos, it makes no sense, reach an agreement about the guitar balance.
Check this link for more EQ ideas.
https://www.thegearpage.net/bo…ock-guitars-live.2009593/
Another take to cut through live in a 2 guitars band, additionally to amp EQ settings (either valve or digital), volume, loud speakers and cabinets, is the type of guitars and pickups. Many 2 guitar bands try to use different guitars or pickup setups, or even different type of speakers/amps, in order to complement each other and don’t compete in the same frequency, giving each a different sound color.
Many examples:
AC/DC Gibson SG + Gretsch
GNR Gibson LP + Gretsch or Tele
Def Leppard, Whitesnake LP+Super Strat
Steve Vai band SuperStrat+PRS
Rolling Stones, Maiden, too. You name it. Just another alternative.