"sandy and thomas " is an example of a subject.

This is an example of a multiple subject. In English, a sentence can have one subject or multiple ones.

Example: John is a very responsible student. (This is an example of a single subject.)

John and Ana are very intelligent students. (This is an example of a multiple subject.)

Other examples of multiple subjects include the following:

My sisters and I played together in childhood.

My dog, my cat, and my bird are the most beautiful animals in the world.

In a sentence, you can have the number of subjects you wish, always that then they are well conjugated; that is, they should be conjugated in the plural form of the verb because they are more than one subject.