Relatives look to you for information and direction. Don't expect them to understand the problem unless they have adequate information about it. Don't expect them to ask for information, either. Take the initiative and give information. They may not want to intrude, but you may think they are not interested.
Information increases comfort.
They may start doing some exploring on their own. Think of them as part of the family team, instead of your having to do everything alone. Explain what your child's problem is, how to act, what it's like for your child, what it's like for you, and what you are doing to help your child. Tell them what you need and what helps. Maybe they know someone who can get it for you wholesale or help build it.