People say readers will read all your books, but I'm starting to doubt this.
I think most readers will read some of your books.
Whenever I do an informal poll, most of my readers have read some of my books, not all. And these are readers who are already on my mailing list or in my Facebook group, who are interested enough to answer a question or fill out a form.
Most people don't go back and read your entire backlist, especially if it's on the longer side (I have 30+ books at this point).
Heck, I had a reader tell me she was "saving" my other books for later, because she wanted to know she'd have something to read. That's sweet of her, but it's entirely possible she'll forget to get to them.
So, yes, I think your books are competing against each other. I try not to run too many ads, on the same platform, at the same time. I perma advertise my two most popular series, but I mostly focus on different audiences, and then I advertise my latest release.
I've noticed when I run heavy ads to multiple books in a series on AMS, I do eat into my profits. So I try to avoid that, except for new releases, or campaigns with multiple targets.
In the grand scheme of things, the competition of your other books is pretty minimal compared to all the other books in your genre. It won't hurt too much to have some audience cross-over, but you do want to keep it to a minimum if you want to keep your ads efficient/have the best possible profit.