If your wife's relative is in permanent receipt of state benefits then he must have been assessed some time ago and diagnosed as unable to work in a 'normal' job because of his condition. I have three grandchildren on the autism spectrum and they are all very different. It sounds as if he is not getting the support he needs to live as full a life as he might. Have you (as a family I mean, not as your responsibility) investigated if there are any organisations in your area which help people with autism? There are in most part of the UK. I know that Barrow is not a very well-off area, but you should be able to get help to make life more pleasant for you and for him. With regard to other issue, many people with autism eat very restricted diets, which may change from time to time, and appear to be very antisocial, but they do not intend to cause offense. Their brains are simply wired differently.

Everyone is on the autism spectrum - it's like the electromagnetic spectrum in a way. Think of "normal" people as ordinary daylight. Asperger's people are akin to someone in the blue and ultraviolet range. They can function extremely well, but also function "invisibly"
We have to teach ourselves "rules" in order to fit in to society, and when society becomes too much (raucous noise, too many strangers, etc.) We need to withdraw into our shells. If we cannot, we can become aggressive or we have a melt-down. We cannot read facial expressions very well, so we cannot read "hints". But we don't mind being told directly. (or at least I don't.)
Most Asperger's syndrome people perform well at logic, hence, given the right tools they make excellent programmers. There are strong indications that Sir Isaac Newton had Asperger's syndrome, and he was definitely a genius. He was also socially awkward and did not like having his work contradicted. That is why he hated Robert Hooke, who had a contradictory theory of the nature of light. Hooke was the president of the Royal Society, and when he died Newton succeeded him and had every single painting of Hooke destroyed, plus all references and accreditations to him.
It wasn't until the second half of the 20th century that the quantum nature of light was discovered - and with it the proof that BOTH Hooke and Newton were correct!
So be tolerant, and when he needs "space" let him get it. But also explain the "rules" to him, with reasons. He does not need medications - he does need a "safe" retreat.
Often, I suddenly realise that I have ignored someone when they spoke to me about a minute ago and then try to rectify it.
Another problem is that when someone asks "Do you want A or B" they expect an immediate answer, or at least an acknowledgement like "I'm trying to decide." The Asperger's person doesn't answer - but give them time. They are thinking and weighing up the choices. After a minute or so they will tell you their decision, usually after you have given up and changed the subject! They are not being rude - it's just the way they are wired.
However, if it is at all possible, get him into a job and (eventually) out of state benefits, which is a waste of a good mind. Does he know any computer languages? Can he fix electrical circuitry?

I have Aspergers and ADD. I was diagnosed as an adult. As s I have said at a few speaking engagements on the subject "if you have met one person with Asperger's/Autism/ADD/ADHD/etc, you have met one person with ..." That being said, from what you have presented I would assume he was diagnosed as a child and did not have a strong well informed support system. Those that are diagnosed at a younger age tend to be less well adjusted. There is no meds for it. The only thing is a strong, well informed support system that will not allow them to settle into their comfort zones. Must be pushed out of the comfort zone 80-90% of the time. Only brief moments to slip back into reset mode. They will not do this on their own, ever.

Understanding his condition does not equate to allowing him to take over your household and ruin your life. A wife should treat her husband like he's the most important man in the world. It seems she is not doing so.

This is a difficult condition to live with. I've seen it up close (starting with many family members including my father). I don't know if you've experienced the "meltdowns" but they are alarming and seem to come out of the blue. I deduced from MUCH reading, these happen when they have a high degree of anxiety. I wish you the best and wish I could tell you things will get easier, but if anything, as they age, the condition becomes more fragile. Thank you for your honest post. It's refreshing to hear from a non-aspie who is struggling. I so with you.

A gluten free diet reduces inflammation and can reduce some symptoms of Autism. I've been gluten-free for 16 years, I wouldn't do it if it didn't help, and I get effects from small amounts of contamination. I know a few other adults IRL who have been gluten-free for a year or more, and all of us have had improvement in our social skills.

But eating that much cereal is horrible for him. I mostly eat grain free and low carb, some 70% of Autistic people are missing the digestive enzymes to handle carbs and sugar properly.

Autism, which ever bit, can manifest itself just the way you have described. There's always the difficulty of separating the condition from a personality but............

Not showing emotion, i.e. gratitude is just an inability to understand social niceties, autistic people just don't get it, it's not personal it just doesn't register and it can be frustrating to be on the end of it. Obsessive behaviours can also occur. They can hear something and just take it to the nth degree, like with the broccoli.

The best bit of advice i heard in relation to communicating with someone with autism is to engage the passion. try talking with him about what he likes to do and feed other bits in slowly. Too much info will lead to an overload.

Check out a guy called Wenn Lawson, he's an autistic guy with an amazing history who is really inciteful in how to approach and deal with and help and support someone with autism.

The other thing you do need in abundance in patience. And like I said earlier don't take apparent rebuffs personally, he may really like the help you have given him but doesn't know how to express it.

Good luck and keep asking, I'll always try and help