Learn Croatian: Uvijek radimo kako god oni žele. - We always work however they want.

Kako normally means "how". Adding the particle god turns it into an indefinite adverb meaning "however", "in whatever way", or "no matter how". So, kako god oni žele means "in whatever way they want".

Can I use kako god to mean "however" in the sense of "but"?

No, this is a very common trap! Kako god only means "however" in the sense of "in whatever way", like in this sentence. If you want to say "however" meaning "but" or "nevertheless", you should use words like međutim or ipak.

Is the pronoun oni strictly necessary here?

No, you could just say kako god žele. Because the verb ending in žele already indicates "they", the pronoun oni is optional. Using it here just adds a little bit of emphasis: "however they want".

Can the word god be separated from kako by other words?

No, in combinations like kako god, tko god, or što god, the particle god must stay right next to the question word it modifies.