to get the brushes in slow motion, you’ll need at least 1/400 excluding any camera movement you’re using.
Also, a camera that can shoot higher than 60 fps will alleviate needing to twixtor anything.
If you don’t have enough light, you’ll also run into the problem of depth of field plus higher iso.
You will need brighter lights or try to bring them closer. i.e. inverse square power of light.