Q. If I am home alone for a meal and my cat is sitting with me, can I still say the line about blessing all those that are seated here?

A. Horav Kalman Ochs Shlit’a maintains that he literal translation of המסובין is guests who gather and partake of the meal which does not apply to animals. 
Horav Shlomo Miller’s Shlit’a opinion is that it is more important to feed the cat or other pets before one eats.
The words you mentioned are not that common anymore in Sidurim and Benchers, however one can usually pray for all possessions that one has.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller, Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu and Horav Kalman Ochs Shlit’a