Get on your hands and knees
The best way to weed a path is to get down on your knees and do it by hand. Use a kneeling pad or a low seat if it helps. Arm yourself with a sharp knife or bespoke weeding blade, and push it as deeply as possible into the gaps, hooking out weeds, roots, soil and all.
If you can't get right down between the gaps, simply scrape the blade along the joint, slicing through weed stems. This will remove moss as well. Use a stiff broom to collect the weeds and soil, brushing in every direction to clear the gaps of debris.