If the noun is singular, use is. If it is plural or there is more than one noun, use are. The cat is eating all of his food. The cats are eating all of their food.

Is this or are this?

If the noun is singular, use is. If it is plural or there is more than one noun, use are. The cat is eating all of his food. The cats are eating all of their food.

Are these or are those?

Similarly, if you the things are close to the speaker you should use “these,” and if they are away you should use “those.” Notice that the time will also influence the usage of “this” and “that” as a demonstrative pronoun. If something happened in the past, the usage of “that” is more appropriate.