What kinship terms to use for spouses of aunts and uncles in same-sex relationships?
Same sex marriage is a relatively new concept to Chinese. Different people may address the same sex partners of their aunts and uncles differently. Most likely people would call them by the general term 姨姨 and 叔叔 like they would call a stranger who is close to their father's age.
I would suggest:

Your (mother's sister) aunt's partner is also your aunt (姨姨) To tell them apart, you can add the last name before 'aunt' If your aunt married a woman whose last name was Chan. you would call her 'Aunt Chan' (陳姨姨)
Your (father's brother) uncle's partner is also your uncle (叔叔). You also call them 'last name + uncle' (e.g. 陳叔叔)

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Your father's sister is your 姑姑, and you can call her partner '(last name)+姨姨'
Your mother's brother is your 舅舅, and you can call his partner '(last name)+叔叔'