Do I need to ask permission to provide a narrative of a scholar's methods?
For writing a narrative about published research in your own words, you need a citation and that's it.
For quoting directly from short passages of published research, you need a citation and indication that this is a direct quote.
For images/figures you likely need permission from the publisher unless the images/figures have been released with a license that allows you to reuse them (you'll have to check for each individual image) or if your use falls under some form of &quot;fair use&quot; (the term is used in at least US and UK copyright rules; similar doctrine may be present in other countries). Writing a textbook you intend to distribute/sell is probably not fair use. Putting the figures in a slide show for educational purposes of your own class probably is.
If you were writing an entire book about one (living) subject I think it would certainly be good manners and perhaps a useful collaboration if you were to contact them and get their blessing, but it would not be strictly necessary to do so. It sounds like your intent is instead to provide narrative research descriptions from many different scientists at an appropriate reading level for your target audience, so I don't think it's nearly as important but you might still find some benefit to reaching out to some - scientists are typically excited to share their work, especially if it's an opportunity to spread their research area to the next generation.
Lastly, I'd urge a bit of caution in your approach. Papers these days are typically written in ways that suggest that science is clean and linear, when in fact it is often messy and circuitous. Your approach seems to make it even cleaner and more linear. It's common for textbooks to take this simplified approach to historical experiments, but it doesn't necessarily convey what science really is to people who may be interested in pursuing it. The conflict in expectations can be quite distressing when it is first encountered.