This tense is called "geniş zamanın hikayesi" which means getting present simple and past simple -r and -di affix together. Some examples:
*Eskiden tenis oynardım.
*Bayramda büyüklerimizi ziyaret ederdik.
Question version:
*Eskiden tenis oynar mıydım?
*Bayramda büyüklerimizi ziyaret eder miydik?
However, in your sentence, that is other form of asking that if the person wants to have a coffee:
Bir kahve de siz alır mısınız?
Bir kahve de siz alır mıydınız?
Although this two sentence almost same, the difference from first sentence is, in the situtation like this:
You are giving coffee to one. And then you are saying to other one:
- Ahh, would you have a coffee too?
(- Ahh, siz de kahve alır mıydınız?)
Basically you can use two of them in the same meaning in this case.