“He is more interested in music than me.” = He likes music more than he likes you! You will hear this construction a lot because it feels quite natural, but it’s not ideal. Consider: “He is more interested in music than I am.”

‎He rather than I is interested in music He is interested in music rather than me The second is more natural but you should say "he is more interested in music than me." Not only can she swim but she can sing He enjoys not only swimming but singing The two sentences do not have the same meaning. The first means she CAN do both, the second means he ENJOYS both. ‎I ate some chocolates with some fruit I ate some chocolates along with some fruit The first sounds more natural but you would probably just say "chocolate" not "chocolates." which one is more natural

Of your six sentences... I don't understand the meaning of #1 or #2. #3 and #4 are both correct. Both sentences would be improved by adding "as well" or "too" or "also": "Not only can she swim but she can sing as well" "He enjoys not only swimming but singing too" #5 and #6 are correct and sound equally good.

Let me try .... He is more interested un music than I do. Not only can she swim, she can also sing. I ate some chocolates and fruits.