a pooltoy, Charge, Cradle, Echo, Kharaya-do, Luna, Meredith, Sevens, Sparkles, Spoke, Taliesenn, Tanwen/Tanwyn, UMBRA. and Vivi
Plural
ΘΔ
Autistic, ADHD
Nonbinary, Genderqueer, Trans
Kinky Ace, Demi, Bisexual
Definitely the latter. It feels like a word that fits having a nonstandard plural form.
Both, interchangeably; usually "'sonas" by default, but "'sonae" once or twice when it felt funnier.