These distinctions are imported from Chinese, where 叔母 and 伯母 are pronounced differently, although nowadays 婶婶 is much more common than 叔母 and both only refer to the wife of the father's younger brother, while 伯母 is an older brother's wife.
There are many more different terms for various fine distinctions of relatedness, but I only know those I had a need to use, and when I asked a Chinese friend for help, he told me that he can't remember all of them either.
Nice to learn that Bulgarian is not the only language that is so precise about relations. However, many of these words are disappearing from usage as families get smaller and younger people don't learn them.
Sister of mother
Sister of father
Elder brother of father
Younger brother of father
Wife of elder brother of father
Wife of younger brother of father
Brother of mother
Wife of brother of mother
Son of brother
Daughter of brother
Son of sister
Daughter of sister
Husband of sister
Wife of younger brother
Wife of elder brother
Sister of wife
Brother of wife
Husband of sister of wife
Wife of brother of wife
Brother of father of husband or wife
Sister of father of husband or wife
Wife of son of brother
Wife of son of sister
Husband of daughter of brother
Husband of daughter of sister
In English, most of these are Uncle, Aunt, Cousin, sister-in-law, brother-in-law, mother-in-law, father-in-law, nephew, niece.