1.mis is 'my', describing my what-so-ever, and here it says 'this room belongs to my sons', with the implication that there is more than one son.

2. él him, in this case dormitorio?

Yes, it means Este dormitorio (to correct your mistake, it's not Esta, it's Este)

3. dos camas two beds. In general, foreign languages don't seem to have quantifiers like Chinese, so you have to choose the right quantifier to translate according to the noun you're modifying.

Su is also used for her

mi and mis both mean 'my', mi modifies singular nouns, mis modifies plural nouns

él means 'he' and 'it', 'he' male when referring to a person, 'it' male when referring to other 'it's', and 'he' male when referring to other 'it's'. , when referring to other 'it's' it should be a masculine thing, like the sun or something.

I think you said 'dos followed by the omitted noun camas right?' It refers to dos in 'Aquél es de nosotros dos,mi esposa y yo.'

Here dos is followed by the explanation that it's mi esposa and yo.

It means 'That room belongs to the both of us, my wife and me'