How to maintain Weed-free patio?

[Wayne2019]

My front and back yard had new patio put in (not sure how deep builder dig, but levelled, laid black sheet, sand, paving)

3 years now, paving loose, and weeds growing

Same weed growing in the back 'cobbled' alley

I sprayed weed killers, but it seems to work on some weeds and not others...

(1) what is best for weed removal?
- cheap weed killers?
- branded weed killers?
- spray late spring?
- butane gas burner?

(2) How best to fix loose paving?
- just add more sand and level ?
- or more or new mortar?

(3) rear alley is small cobbled stones with weed/grass/shrubs (pic attached)
- how best to remove?

Thanks all
Wayne