ἆρ᾽ ἀκούετε
οἵας ἑορτῆς ἔστ᾽ ἀπόπτυστοι θεοῖς
στέργηθρ᾽ ἔχουσαι
Eum. 190-191

How is ἔχουσαι being used in this sentence and is ἔστ᾽ second person plural or third person singular?

ehousai seems problematical here, because there is no obvious (plur-fem) subject. Yet, there is help, in the opening verb, ‘akouete’ (you listen). This ‘you’ is also the subject of ehousai and refers to the Chorus of women. Another trouble comes from the need for ‘stergithr ehousai’ to be understood as a single word (love, like, tend to, embrace, etc). Est is plural sec. person. I think the whole meaning becomes clear enough if you change the word order:

ἆρ᾽ ἀκούετε
οἵας ἑορτῆς στέργηθρ᾽ ἔχουσαι
ἔστ᾽ ἀπόπτυστοι θεοῖς

so would you translate it thus?

" Can't you hear for what sort of feast you are abominable to the gods because you embrace them?"

I would try to follow the original word order if possible. E.g. "Can't you understand, for what feast abominable you are to Gods for your liking?

This way, the feast essentially surrounds the reaction of Gods, giving emphasis to the initial suprise at the kind of the feast (can't you understand?)

so you are translating ἔχουσαι as a causal circumstantial participle?

Are you suggesting something different?