The heresy of Modalism denies the individual personhood of the 3 PERSONS of the trinity THREE SEPARATE PERSONS YET ONE..
Yeah. Mary was only the mother of Jesus’s human nature. Right?
Not persons. Hypostais is not a "person." Modalism comes form the Latin mistranslation of Greek into persona, which in Latin means a mask. Thus, some Latin Chirtsians believed God was merely carrying different masks as he revealed himself. Unfortunately, western Christianity never corrected the mistranslation and so "persona" became a theatrical term in English, while the Greek term hypostasis became a "person."
Literally, hypostasis (sub+stasis) means something that stands on its own, i.e. sub-stantia, something that exists on its own, in Greek o ΩΝ (literaly the existence), a self existing or hypostatic reality. There is no personality imputed or implied in it. It's an insult to God to call him a schizophrenic deity, a multiple personality God.
Of course, Latin managed to complicate things further by (illogically) incorrectly translating ousia into substantia (or substance, matter), further corruption the concepts, especially given the fact that ousia in Greek means essence or nature and not necessarily matter.