"These are my cats."
Translation:Das sind meine Katzen.
i had a similar doubt for another question. This is the reply I got. Hope this helps.
"You can't use "diese" here. You can use "dies sind" (uninflected) or "das sind". As a rule of thumb, you should refrain from using "diese" as a pronoun (on its own). Use it only as a determiner (followed by a noun)."
I think in this case, you can't use Diese because you are introducing it for the first time. Whenever that happens, you generally want to use the general or uninflected form. Now if I were to say "These cats are eating fish", then I could say "Diese Katzen fressen Fisch". When I say like "This is _", then I would say "Dies ist (or any conjugation of it) ____". So I guess if your verb is only "to be", then your "this/these" should be "Dies". I hope that helps!
Meinen is generally used in the accusative form (when it is the object), and it only applies for objects that are males. So if I were to say "My cat likes my dog", then it would be "Meine Katze mag meinen Hund". Notice that the first my is "meine" because it is the nominative (and it is meine instead of mein because it is feminine). The second my is "meinen" because it is accusative (if the object were female it would be "meine", and if it was neuter then it would be "mein"). Hopefully this helps!