That is a toughie! It may work--IF--you cover the good bushes with a plastic bag. Spray with vinegar, hot steam, exhaust from your mower, ammonia, whatever you can think of.
Then with rose pruners or scissors, cut off new shoots of the knot weed every week to keep it less than 6 inches tall. You may wish to use Octane or Quicksilver--both are about a hundred times safer than Weed B Gone. You only need about 3 milliliters per gallon.
If this is not practical. Remove bushes. Kill whatever you can and lay sod. Keep cutting it short. Plant bushes in big decorative pots.
Just my opinion...YMMV.