Euphorbia bupleurifolia you won’t have to worry the leaves will shed. The E. flanaganii I’ve never thought about pruning, but I’m sure you could just cut whatever branches you didn’t want, to keep it from getting big. I’ve seen some branches get pretty long, but others not so much. Personally I would just leave them be;).

Last winter my bupleurifolia didn't lose all its leaves (first time in 13 years). I just let it do what it wants, when it wants to.

Thanks! It’s the flanaganii that I was more wondering about, for now the plan is to leave them and see what happens