How hard is it to add to your family of pets?

I agree with Ram.

Sometimes older animals like the companionship of new younger pets and other times they get jealous or get irrated by the newer ones wanting to play.

Older animals usually think you belong to them and often can get mean or rough with newer pets, or may become sad and depressed when a new pet arrives.

It would be better to try one at a time to see how your current pets behave.