I have no evidence that they are, in fact, stealing the Property of the American people at the White House. This is really something that is probably being looked at by the people who run things at the facility. There are clear rules for what is, and what is not, the property of the Trump Family and what belongs to the government.
The thing is, I do suspect that the lines are blurred because the Trump family has behaved as if everything in the White House belongs to them. Anyone who tells you they have proof is probably lying to you.