Try letting the cousins take something of your huspand's away and then see how generous he feels. I'm sure he'll have a few of his own 'toys' laying around not being used. Would you allow adults to go through your things and then give in to them wanting to take stuff home?
We do tend to use those excuses as 'too many toys' and 'they're not being used/played with any more' but it is wrong to give away something that belongs to your kid. Let them make the decision then respect it.
Are the cousins just as generous and sharing? These things are often one sided.
