Hard to be definitive without being there but maybe something a bit stronger like stump killer roundup super concentrate..I use it for stubborn stuff ..should make it a lot easier to then pull out...would be nice if u could level it off...cobble it and some nice decorative pots etc
Ps it would...
If these are just your basic weeds that you can’t pull out then gallop 360 (it’s what I generally use on sites) is good enough..bramble etc then something a bit stronger..photo?