Is there a language in which a relative clause can refer to two different elements of the main clause?

I must admit I don't understand how that would work. I have not come across that idea yet.

I can tell you that there are languages that have relative clauses but no relative pronouns/conjunctions, such as Japanese. I bought the book (that/which) he wrote, in Japanese is: I he wrote the book bought. (very roughly)

All adjectives in Japanese, whether they are true adjectives or relative clauses, go in front of the nouns they modify, and therefore do not need a relative pronoun/conjunction.

There can be more than one relative clause, but they would all modify the noun that follows the last relative clause.

Of course, there are thousands of living languages alone, so there may be languages with relative pronouns that work the way you suggest.

Wow, that is a really interesting question. I would bet that some, or most, languages that use what's sometimes called "4th-person" pronouns can do this. That is, there are two versions of "he," or of "she," or of "it," that you can use when saying "Tom and Bill were talking, and HE told HIM....." and you'll know which one refers to Tom and which to Bill, which is not possible in English.

If a language has a third-person "he" and a fourth-person "he," I bet it also has two different relative pronouns, too.

("Fourth person" isn't really the technical term for this, but it's commonly used. These things are really called "proximate and obviative" pronouns. You can use the term "obviative" to look this up in linguistics books.)

Some of the Salishan languages of British Columbia and Algonquian languages of eastern Canada and USA have the "obviative" feature.