I would use the word would if I could is one example
Yes, I can use "his" twice in a sentence: He gave his dog his favorite toy.
Once bitten, twice shy.
I have not yet had the opportunity to use have twice in a sentence.
The word 'just' used twice in a sentence: Twice I left him a message and twice he ignored me. The term 'just twice' used in a sentence: I've only been here just twice before.
There is an equiniox twice a year. There is an equinox in March. There is an equinox in September.
There is a mouse over there by the door.
atoms are apart of everything in the world!
I have endeavored the darkest parts of the world.
It is a fallacy that the world is flat.
"I envision a world where violence is not an issue.
I'veno fluency in that language.
Yes, it is possible to use a preposition twice in a sentence if the sentence structure requires it. For example: "He walked up to the top of the hill." In this sentence, both "up" and "to" are prepositions.