שניהם - both of them
שנינו - both of us
שניכם - both of you males
שתיכן - both of you females
Also works with other numbers - שלושתם, שלושתינו, שלושתכם, שלושתכן
I think one will use it until five or so, after that it sounds weird.
Is the ה silent in הולדת ? I hear " yom (w)iledet "
( which just happens to be the exact Arabic meaning of "the day of birth of" ! )
They are actually very often not pronounced. Glottal stops (א and ע) are also often dropped as well.
2 The glottal consonants are not usually pronounced, as other than in careful or formal speech they are normally elided in unstressed syllables, and sometimes in stressed syllables as well.
The cited reference is of a study of colloquial Hebrew published in 2014.