I would wrap the Echinopsis with towels and then have someone help you hold the stem and lay it on the ground and then remove the pot. If youre not attached to the pot, its easy to get off by just breaking the pot.
The opuntia, if it was me you have a few leaves that droop down those I would prune off which will make repotting it and stabilizing it easier during the whole process and its basically the same process as the above. You can then just propagate those that you cut off.
It's definitely not hard enough that its impossible you just have to be careful, and cautiously expect it to not go as planned. You got this, you can do it!!
