you mean Lispen is the real broher of Lidusis?
Σ(  ̄□ ̄||)
no lispin is/was a caretaker. And lidusis only brother is the brown haired guy/ it shws,in the earlier chptrs, that lispins been around the brothers since childhood.
most likly correct if not then that means lidusis brother didnt know that lispin had his own "secret" plan going on. Also i think lispin is the "betrayer" they were talking about (but these r just my thghts gathered up after looking at all the other comments) :/
If he is they havnt showed any signs in the manga/ so far its only shown that hes a care taker.
(also my own thoughts- i think lispins been playing for diffrent teams in disguise. cause
1. lidusis mother,i think, got lispin into the acadamy/which hes either working for the ma
2.lidiusis brother also told lispin to watch lidius/in which hes working for lidusis bro
3.lispins on some not yet known team/ which might b just b 4 himself OR
4. Hes in leage with all three of them/ in which case the mas been pretending to be good or lidiusis bro was pretending to be bad) though this is all just guessing :/

Was that Lidusis' brother or Lispen (his guardian?) who was killing The Tower magicians? And working with the dark entity?
Is Lispen Lidusis' brother?