@Sleepneededprettyplease I'm not a legal eagle but to me, he has no claim on the house and I would have thought he has shot himself in the foot here.
Am I right in my interpretation that there are two houses, the one your aunt lived in alone and the house she put in your name for the benefit of you and your sister? He has been living in the house that is legally yours and he is claiming he was a dependent of your Aunts?
Based on your explanation, he is not a dependant of your Aunts because it is legally your house and that is why he has legally been told he has to leave! Your Aunt cannot gift occupation rights in a property she does not own, she can ask you but she cannot legally grant permission herself. So the lodger was living there only because you allowed it, whether explicitly or tacitly so his argument against your house does not stand and he has no right to remain after her death unless you let him. Just out of interest, did he know the house was in your name prior to her death?
So lets then look at the house your late Aunt lived in and owned.
To be considered a dependent under the Inheritance (Provision for Family and Dependants) Act 1975, he would need to show that the the aunt was maintaining him financially, on a regular, ongoing basis, and that he was unable to meet his own reasonable needs without her support. Simply living rent‑free in a house she didn’t even legally own does not meet that threshold. He wasn’t being supported by her assets — he was occupying a property technically owned by you. That is a big difference to his argument. I suppose technically, anyone can submit a claim. But the real question is: would it succeed? And I agree with your solicitor, the answer is no! Based on what you’ve described, the answer is no because I can't see that the court would let him win purely because he says "“I lived there for free so I should get to stay”. And lets not forget that her Will clearly states who her beneficiaries are.
Being realistic, technically he was never financially dependent on your Aunt as he was in YOUR house, and he can't claim against her home as he wasn’t living in her property, he wasn’t part of her household, he wasn’t her spouse, partner, or child, he wasn't maintained by her (unless of course she contributed financially but even then its a long shot) and he has no contractual or tenancy rights.
He is a chancer, he is putting in the claim as he wants the gravy train to continue and at the very least he hopes that purely for his nuisance value, you will give him something to get rid of him and avoid court costs - do not give into him. He has had the benefit of free accommodation and he should be very grateful for this and now leave the family to deal with their grief.
So in short he wasn’t living in the aunt’s property, he wasn’t financially dependent on her, and he wasn’t part of her household. The house he’s in belongs to you, not the aunt, so he has no right to stay and no realistic claim under the Inheritance Act. YOU ARE NOT BEING UNREASONABLE STAND YOUR GROUND AND GET HIM OUT. He can file a claim if he wants, but it won’t succeed