The first day פיוט לסוכות, (Shachris before Kedusha — אקחה בראשון) we say:
“כְּאִמָּהוֹת שְׁתַּיִם” (like the 2 mothers)
“כְּגִבְעוֹת אַרְבַּע” (like the 4 mothers)
My father a”h, while in Shul, was troubled by this question.
He looked in the מטה לוי who explains that the 2 mothers are Leah & Rochel.
He came up with his own Pshat that the pronunciation should be KeAmhos with a patach.
When he came home from shul, he checked in his Heidenheim Machzor, that he kept at home.
Instead of a חיריק under the Alef, it is a פתח, referring to the two maids זלפה & בלהה.
I had the opportunity to check out an old 14th-century handwritten Machzor.
In this Machzor it does indeed say KeAmhos with a פתח under the אלף.
but the two maids: זִלְפָּה וּבִלְהָה