Responses
Hi, first of all thank you for your hardwork translating this for us to read.
I'm "keep source format" team so if uncle part is deliberate then uncle it is. Keeping shushu is also okay, because to me at the end of the day they're still couple who's family on legal papers AND with large age-gap. (Personally I think author is deliberate to make this weird LOL)

I just reread the raws, it seems like xie Liao is indeed referring xie fengtong as “uncle” (not mister) when he calls him shushu (叔叔)
Do you guys prefer if I continue to translate the 叔叔 as “shushu” when xie Liao refers to xie fengtong as that or should I change it to “uncle”