"Your letter to them was sent two weeks ago."

Translation: Surat Anda ke mereka terkirim dua minggu yang lalu.

[Elizabeth693356]

Or is "kepada" better than "ke" ?

[UpzahwvW]

Yes, kepada is the appropriate choice. "ke" is for non-persons.

[donny309620]

Is "untuk" better than "ke" in the sentence?

[UpzahwvW]

Yes, "untuk" would also work in place of "ke"