And now to explain what we started (regarding 'Gilgul Kaful'), as the pasuk says, "פוקד עון אבות על בנים." (Hashem visits the sins of the father on the children.) To explain this, until three Nefashot (referring to the three chances a Nefesh has). When the Nefesh was new [in his first life], he is able to reincarnate alone in a body from the day it was born, and [I could be translating wrong here, but it appears that it says that the reincarnation can be in a way where there could be FOUR Nefashot together in a body, and this is the secret of "על רבעים."
Alternatively, this could simply be referring to the 4 lifetimes, meaning the three reincarnations, or three chances a new Nefesh has to do a mitzvah before it is considered a Rasha and is cut off from kedusha.] This is also the secret of 'three times to overcome', because [again, maybe I am mistranslating here, but it appears to say that] three Nefashot are able to be reincarnated into one person, and this is the new Nefesh (which has on top of it three more Nefashot).
However, more than this, it is not possible for them to reincarnate together (into one body). However, it is possible for it to be less than this calculation, because it could be that one Nefesh along is reincarnated into one body, or one Nefesh is reincarnated with another new Nefesh into one body, or two Nefashot are reincarnated together into one body, or two [Nefashot] who are reincarnated with a new [Nefesh], or three [Nefashot] which are reincarnated together, or three [Nefashot] who are with one New [Nefesh]. However more than these calculations, it is not possible to enter into one body, as we described.