The sentence structure containing a relative pronoun indicating the indirect object in the clause

When you want to indicate an indirect object with a relative pronoun, you might change the sentence structure from "verb + IO + DO" to "verb + DO + to IO. But this conversion may be unnecessary. Which is comfortable, acceptable or wrong among the sentences below? Does it depend on formality? Let me know what you think.

1. There were two healthcare workers who I handed the paperwork to.
2. There were two healthcare workers who I handed the paperwork.
3. There were two healthcare workers to whom I handed the paperwork.

IO: indirect object
DO: direct object

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As John kindly commented, it may depend on the verb. Therefore I added two more sentences below.

4. There were two healthcare workers that I gave the paperwork.
5. There were two healthcare workers that I gave the paperwork to.