"Bonvolu kanti, ĉar via fratino ankoraŭ kantas!"

Translation: Please sing, because your sister is still singing!

[Novantico]

Seems like kind of a weird sentence.

[theabigaillo]

I interpreted it as "Please sing, because your sister is still singing and God knows she's much worse than you! In fact, she sounds like some variety of dying animal! So please sing, for the sake of our ears!" (First reaction was "Wow, someone just got wrecked.")

[das-g]

Weird logic at least, lest we know the context.

[hellomidnight]

Pride and Prejudice

[sousquark]

Bonvolu kanti is “Please sing”. Would “Sing, please” be Kantu, bonvolu?

[Salvesen]

No you can not have a u ending on both words. It would be kanti bonvolu

[TomDouglas9]

I'm curious if you could use "... via fratino kantadas" or something like that. [If I have the wrong suffix, I meant the one which means "to continue to".] Dankon.

[das-g]

I'm curious if you could use "... via fratino kantadas" or something like that.

Yes, that's possible.

[If I have the wrong suffix, I meant the one which means "to continue to".]

-ad- is probably indeed the suffix you're looking for, though it doesn't exactly mean "to continue to". It does put focus on the duration an action is (often continuously) performed.