Drush 5 & 8 side-by-side
Yes.

alias drush5='~/drush5/drush'
alias drush6='~/drush6/vendor/bin/drush'
alias drush7='~/drush7/vendor/bin/drush'
alias drush8='~/drush8/vendor/bin/drush'


You will get help from Switching Drush Versions.