Thank you. I am going to assume the son is an adult.
This is not quite right. Without the son's permission, his things cannot simply be "moved." He is what is known as a tenant at sufferance, meaning he is a tenant who lives on the property at will of the owner.
The owner(s) have to formerly EVICT him to get rid of him. By an owner simply taking his items out, this is unlawful and constitutes an unlawful eviction and trespass to chattel (when one is interfering with the ownership of other's items). This opens someone in your situation up to LIABILITY.
Ergo, I would avoid doing this favor, as it has the potential into turning into a big mess.
(I notice that you state "without her knowledge and consent," so did you mean the wife not knowing? If I have misunderstood the situation, let me know.)
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