Well, extracting pure alkaloids, if you're thinking of getting pretty white crystals, is usually very difficult. Chances are you'll be left with something gooey or oily, so wouldn't advise it if you're trying to lay it onto another herb.
Copypasted this tek from another site:
Extract 3 times with 0.05 M H2SO4
Defat 3 times with hexane (naptha will also work in this case)
Bring pH back to 11 with NH4OH (this can probaly be replaced with NaOH I see no reason why not)
Extract basic solution 3 times with DCM (this can probably also be replaced with toluene I would not recommend naptha or hexanes for this step as mesembrine is not very soluble in them)
You will be left with a brown/yellow oil containing mostly mesembrine and a few other alkaloids depending on the plant material, when it was harvested, and how it was processed. Now pure mesembrine freebase is an oil so if you want crystals you are going to have to make a salt. I have no information on this process. I also have no information on the safety profile except that sceletium is a very safe plant so I do not see why the alkaloids in crude form will be much more dangerous but please be careful with doses and salts as not much is not known about how the salts effect pharmacokinetics and dose etc.
The yield should be somewhere around 1% (I believe thats the concentration of alkaloids in good quality material.