Answer: The plan the other two rioters make is to play-restle the young rioter when he returns back with the supplies and then stab him to death.
Explanation:For example in lines 225 - 229 it states
" Now look; when he comes back, get up in fun"
" To have a wrestle; then, as you attack "
" I'll up and put my dagger through his back "
" While you and he are struggling, as in game; "
" Then draw your dagger too and do the same. "