Translation:These birds are singing, and those birds are sleeping.
To me it sounds more natural, for a female plural, to use האלו or הללו. But I believe using האלה is also correct (yet, less natural to my ears..)
It might sound less natural to you (you and me both), but it's definitely much more frequently used nowadays, especially by the younger generation.
I guess that all of these options should be accepted
So this could equally well be, "Those birds are singing, but these birds are sleeping?"
Yes. Those and these are determined by context, or gesturing if you’re there in person. And, I’ve translated the sentence both ways in review exercises, and when interchanging these and those in the sentence, either order is accepted as correct.
Btw - Yashan in Hebrew means old as in SOMETHING old, not SOMEONE old. When you want to say that someone is old you will say Zaken(m) / Zkena(f). Yashan(m) / Yeshana(f) will be used for instance when you want to say that a record is old.
For that matter, if you want to say 'The birds are old', then you should say - 'הציפורים זקנות' / Hatziporim Zkenot
So האלה is used for both these and those? There aren't two different words?
“These” and “Those” are determiners that are attached to “definite” nouns. When the noun is definite, the words “this/that/these/those” take a ״ה״ just like the definite noun. Here’s the explanation found in the Tips and Notes in the Determiner lesson:
To say "this dog", we put זה after the noun, as if it were a normal adjective, and it requires ה, like other adjectives:
this dog = הכלב הזה this cow = הפרה הזאת