I would like to compare rennet capability under various conditions. The issue is, I don't want to use calf rennet, but I can't figure out if nettle and syconium, which also coagulate milk, contain regular rennet or other enzyme? If so, what is its name? It's quite important. Thank you.
Any protease enzyme should be capable of causing milk to coagulate, or prevent gelatin from setting. Examples such as papain and bromelain are all cysteine proteases, and all of them will cause milk to coagulate.
The example of fig protease that you mentioned is a cysteine protease (no specific name found, referred to in scientific literature as fig protease). Nettles are a highly polyphyletic group, and the specific enzyme cannot be named without a more specific phylogenetic group being identified.