It's great to see that you are interested in making your characters more diverse and inclusive by exploring conditions like Autism and ADHD. It's important to approach this topic with sensitivity and respect, so I'm glad that you are taking the time to learn about it.
Firstly, it's important to note that you do not need to diagnose your characters with these conditions. In fact, it's best to avoid using labels like "autistic" or "ADHD" to describe your characters. Instead, focus on their individual traits and behaviors that may be associated with these conditions.
To do this, you can research the symptoms and characteristics of these conditions and incorporate them into your characters in a realistic and nuanced way. It's important to avoid stereotyping or portraying these conditions in a negative light. Instead, aim to create well-rounded characters who happen to have these conditions, rather than defining them solely by their condition.
You can also consider consulting with individuals who have these conditions and/or professionals who work with them to gain a better understanding and avoid any unintentional offense.