Just fyi, there are spineless bridgesii & your cacti look about right to me. Of course, IDing a Trichocereus from internet pictures is tricky & the taxonomy is a mess anyways.

A simple tea works really well, 3 15 minute boils each with fresh water, then combine & reduce to a drinkable amount of liquid.

Also, you don't have to starve them if you don't want to, this is to stress them to increase potency but the cactus will still work fine if you skip this step as long as it is potent. You could also increase potency after cutting by putting the cut section in a dark closet for a couple months.