I grew up with a disabled aunt who lived with us. She is physically and mentally disabled, so I've always had a soft spot for people in those situations.
I sincerely, with all of my heart, wish there was something I could do to ease the stress of people raising autistic children/adults. It is real, and seriously hurts many many good marriages. Last year, we moved from Colorado to Texas to work at another church here. Part of the reason I took the position was their strong support of and ministry to special needs families. We have dedicated an incredible amount of resources to supporting special needs individuals and families, and have quite a few scalable options. Even just giving the parents 90 minutes week to be normal people, knowing their kids are in a safe, understanding, and compassionate place is HUGE.
My area often sees young adults with special needs, in their 20's and 30's, who are trying to be as normal as they can, often on their own for the first time. That comes with quite the learning curve for us all, as everyone is unique. It is very difficult, as sometimes they are more like middle schoolers than 30 year olds, and can really change the dynamics of a room (especially when single girls are there). However, we have built a strong culture of patience, care, and understanding, and I'm so proud to see all of our young adults welcome anyone into the group. They help to hold the standards, and proceed with grace. It's amazing to see how it helps people to have a group of people that will treat them just like anyone else, and love them unconditionally.
OP- I hope you are able to have good conversations with the neighbor, and find a solution that protects you both. I feel for you. It's hard. But it really does take a village to support families of all kinds.