Translation:My friends have not spoken with him since Tuesday.
Aidan, desde que requires a phrase with a verb, for example desde que se murió su madre - since his mother died. Desde el martes - desde is a preposition with an object, in this case, martes.
How do you make the difference in Spanish between "since Tuesday" and "since the Tuesday"?
In Spanish, the days of the week need the article. Since the Tuesday in English needs more of an explanation, eg. since the Tuesday her mother died (maybe a week or a month ago). ...desde el martes cuando murió su madre.
Mine used the abbreviation for Tuesday. (Tues.) and was marked wrong. We write itvthat way frequently.
That is fine for casual e-mails and texts but not otherwise. You wouldn't usually find it in the body of a business letter, for instance.
él is not a direct object pronoun, but an object pronoun following a preposition, ie.not direct.