The answer to that question can be Jullie namen zijn Willem en Roos but as the question goes "Zijn jullie namen Willem en Roos?" it is not the right answer.
The spelling of Dutch r varies a lot, even among the same family. It might be a guttural French r (Duolingo uses that), a rolled Italian r, a tapped Turkish r or a subtle English r.
Every one of these spellings are normal and should be accepted.
On national television you'll most likely hear an "English R" when the r is followed by a consonant or the end of a word (example: werk/water), and an "Tapped R" (which is a lot like the tapped t's in "butter" in AE) when it is followed by a vowel (example: trap/kleren)
If it's a listening excercise yiu cannot, but you can if you are asked to translate
Names are a bit confusing: In some exercises Willem is translated to William, in others it isn't. Consistency with this would make it easier.
An earlier usage of the name Roos in a Dutch sentence was spelled Rose, was I supposed to be marked incorrect during a listening excercise for spelling it Rose?
You're being tested just as much on vocabulary as you are grammar and overall meaning. Duo tends to prefer translations that are as literal as possible (while still being grammatical in the target language). In ordinary conversation, "Are you Willem and Roos?" means the same thing as "Are your names Willem and Roos?" but you need to show you know what "zijn" and "jullie" mean.
The correct answer is not accepted. The reason given is that a wrong word was used but my answer is the same as the Correct answer
Because Duolingo will think you're mis-matching their names.
If Duo asks you to translate X and Y, then translate X and Y. Don't translate Y and X.
My answer was marked wrong although it was exactly like the then given "right" answer. How can that happen?
Duo glitches sometimes. Alternatively, are you 100% positive you didn't make a typo that you're just not seeing?
I have been writing the sentence correctly many times but you are reading it wrong. I think you have a bug
Saqué mil veces mal esto solo porque no ponía la doble oo; es una pendegada! Ahí sí deben avisar cuando se nos está olvidando algo superfluo como una doble oo en un nombre propio. NO ES error gramatical ni morfológico ni fonético ni nada.