Prepare him as much as possible in terms of what to expect from your home situation and from your kids. Tell them about your kids' habits and tendencies so he won't be surprised when, for example, one is really messy and the other tends to be loud.
I also second the ideas on quiet space and providing structured activities with the kids, though I'd be wary of scheduling too much as once as this could lead to him feeling overwhelmed and burnt out.
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Given a “tentative” diagnosis as a child as I needed services at school for what was later correctly discovered to be a major anxiety disorder.
This misdiagnosis caused me significant stress, which lessened upon finding out the truth about myself from my current and past long-term therapists - that I am an anxious and highly sensitive person but do not have an autism spectrum disorder.
My diagnoses - social anxiety disorder and obsessive-compulsive disorder.
I’m no longer involved with the ASD world.