It's difficult to say without the actual cello/bass sounds, but I'll give it a go.
My first thought is that if you are going for some interesting dissonance, don't make the players in unison rhythmically. An important part of writing with dissonance, as I was taught, is how the notes sound in relation to each other. So a foreign note played in a space where other notes are held, or no notes at all, is far more powerful than that note being played in a chord.
Also it's a duet! If I wanted block chords, I'd listen to a solo piece!

Remember that string instruments CAN double and sometimes triple stop. Use that to your advantage! Also remember range. Cellos and Double Basses have the biggest range out of the string family, so utilise all of it.
So in conclusion:
Don't use unison rhythms, unless they're fleeting!
Think about the harmonies and whether they'll work better together, or in relation to each other!
Use the instruments you have to their full advantage!
TubeyouYou are the hero My Little Remix deserves, not the one it needs.
So we’ll hunt you. Because you can take it. Because you’re not our hero.
You’re a silent guardian of music, a watchful protector of songs.
A doctor of dissonance.
-Phillypu