Translation:Do we sleep in your bed or in my bed?
So why exactly is, "Will we sleep in your bed or my bed?' a wrong answer when, "Shall we sleep in your bed or my bed?" is acceptable?
Edit: three years later, I turn to Google for insight. From Oxford dictionaries: The traditional rule is that shall is used with first person pronouns (i.e. I and we) to form the future tense, while will is used with second and third person forms (i.e. you, he, she, it, they). For example: I shall be late.
'Shall' only is correct, for the simple future. The correct convention is that, for the simple future 'shall' is used for first person singular and plural; 'will' being used for the other persons. For the emphatic (or 'coloured' [Fowler]) future, the usage is reversed. "I will do it" meaning, "I will that it be done".
Some verbs, such as dormir, are irregular and have different conjugations. When I took Spanish at school, teachers always said basically "sorry these are different, but basically you just have to memorize the exceptions." While that can be okay sometimes, it's admittedly difficult on DL since they don't give you explanations. Here's a list of common irregular verbs: http://spanish.about.com/cs/verbs/a/conjug_index.htm
Because the sentence "we slept" is past tense, referring to an action that already happened. Dormimos, in Spanish, does not refer to past tense actions. It usually only refers to actions that are currently happen, or are about to happen. English has verb tenses just like Spanish: I slept, I am sleeping, I will sleep. These all refer to different points in time. Spanish is the same: yo dormí, yo duermo, yo voy a dormiré.