These are ways to help all children feel important, even if one child is on the spectrum.
Make a date for you to spend time with your other kids to make them feel important, this can be once a week or once a month. Do your best not to miss that appointment. See it as a must instead of cancellable.
Let the siblings be involved as much as they want with the child with autism. Know what there will be times when they may be more involved than others, or simply not involved at all. Older children may have more of a heavy load as they take on more responsibilities because most of the attention is going to the child on the spectrum. Remember to also let kids be kids by allowing them time to play without having care-taking or household responsibilities at all times.
If you want more insight and tips from a sibling’s perspective, I recommended the book, A Shot of Hope, by Zack Peter.