Does the son's statement to his mother, "Yes, I worship money," during an argument, expel him from the fold of Islam, thus necessitating that he renew his pronouncement of the Two Testimonies, or does this statement lend itself to interpretation given that it was uttered in the context of an argument?

Your son erred by quarreling with his mother, and this is an act of disobedience (ʿuqūq). He also erred by saying: "I am a slave to money." However, he is not judged to have committed major disbelief (kufr akbar) that expels one from the faith. His statement is not akin to insulting Allah and His Messenger, and confusing the two is ignorance. The meaning of "slave of the dinar and the dirham" in the Sunnah refers to someone who loves them and is eager to collect them. The use of "slave" here is metaphorical, for the purpose of a simile and attribution.