Due to geographical different, the calling custom can be varied in different China district, especially north versus the south.
In southern China Guangdong region custom, when greeting, the minor always call senior aunt(father side） husband as "姑丈". （for mother side aunt husband is called 姨丈) When the minor introduce/refer their aunt husband to third party, they can use either "姨丈" or 姨夫. Although the books say they are the same, but in vocal speaking , yi^2 zang^4 rhyme is pretty clear, compare to yi^2 fu^1. OTH , Beijing (Northen China) may use different custom.
Since the Chinese rank of 姨 also carry few more meaning. I.e., husband may refer his sister-in-law as 大姨子、小姨子。And the husband will refer sister-in-law husband as 大姨夫, 小姨夫. But since they are same seniority rank , thus, the husband will never call them 大姨丈.
Now come to the next part : To differentiate the husband sister-in-law title versus the husband senior aunt. I.e.
我那个大姨夫 can means "my aunt(father side) husband" or "my sister-in-law husband". Due to the seniority calling custom, 大姨丈 always means my aunt husband.
The person must clarify explicitly during conversation to clear the confusion if they wish to use姨夫 , for example, one will say : 我老家那个大姨夫 my family-side aunt husband. This is important whether in vocal or writing.
When refer to sister-in-law husband, one must first introduced, 我大姨子的丈夫 My sister-in-law husband。
Only after the explicit introduction, the conversation can abbreviate to 姨夫.
So if you are not sure, just ask for clarification. Even Chinese will get confused of those title if no clarification is made.
