Jag vill passa på tillfället och tacka er för att ni är två av de mest ....

(the sentence seems like an interrupted one)

En variant på Lenas förslag. Skillnaden är att jag tror man vill tacka för något som har skett, inte något som pågår.

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I prefer the second answer myself. What I really wanted to add, though, was a comment about the end of the sentence. with the "more" sitting there, it implied that the continuation will be something like "the most wonerful.../the most helpful...". The assumed translation would then be to continue "två av de mest underbara", which you don't say. It should read "två av de underbaraste...". My point? I don't think "mest" is part of a proper translation.

It's difficult, not knowing the whole context, but I feel this is both a literal translation as well as a common way of expressing a more formal way of saying thank you in a letter in Swedish.

Humble question