"My uncle has walked on that street."
अनुवाद:मेरे चाचा उस रास्ते पर चले हैं।
That is a norm in Hindi to show respect for elder persons.
"वे मेरे पिता हैं.वे एक शिक्षक हैं." literally written as "They are my father. They are a teacher." while it really means "He is my father. He is a teacher." The respected form of grammar (which is plural like usage of verbs and pronoun) is used with elder persons, people at high position teachers, doctors ( strangers), husband ( or anywhere respect is implied.) For the case of parents, grandparents, uncles it's always true by context that they (parents, grandparents, uncles) will be elder than the speaker. So, Plural like grammar is used with them. You can use singular like grammar in those context which will be perfectly correct in grammar but that will sound seriously rude. (Don't try that in real life. :P)