is окна one of those irregular plurals? like город - города?
No. numbers 2, 3, and 4 require the genitive singular.
The genitive singular ending for neuter nouns is "-а".
Additionally, the nominative plural ending for neuter nouns is also "-а", so "Окна" is a very regular plural as well.
It wouldn't accept "In a room there are two windows."
Since кровать is at the beginning of the sentence it's more likely to be "the room".
Also, this course prefers English sentences of the form "There is/are X located at Y" to the form "Located at Y is/are X". Not sure why but I suspect the latter are not quite grammatical?
On which syllable is the stress placed in the word окна? Thanks!
Probably a bit late, but it is on the letter а. One way to tell is that when you hear окна you can tell the o is pronounced as a. This is because unstressed o is pronounced as a.
In the room, two windows
I would have translated this as "The room has two windows." Is this also reasonable?
I wrote the number 2 and it declined it, i think we should be able to write the number instead of spelling it
That idea misses the whole purpose of this course. Learning a language means to obtain the ability to read, spell, pronounce and understand both words and numbers. Even the exercise is called "Time&Numbers"