You can read eBay's policy on the sale of stolen goods here: https://www.ebay.co.uk/help/policies/prohibited-restricted-items/stolen-property-policy?id=4334&st=3...
Basically, you need to report it to the police. eBay probably won't discuss it with you, but state that they will work with law enforcement agencies.
eBay is supposed to have a procedure for liaison with the police, but one member told us that his local police didn't know anything about this. So it may be worth mentioning this when reporting to the police.
Addendum! Sorry, I've just re-read your question and had overlooked that you and your ex-wife jointly own this property. In that case, the advice above probably won't apply. It's much more complicated and I doubt the police will even get involved. You need to start by seeing a solicitor, or Citizens Advice might be able to offer guidance.