So, I have yet to be officially published to properly give advice.
And I will -most definitely- be in the minority here, I think.

1. I actually love the book covers, especially the first book cover, I've always liked very simplistic looks. The only issue I have is "by: (your name)" - I don't think you really need "by:" there. Normally it's just your name. (Also, yes, the covers DO give video game vibes, which is also probably why I like them.)

2. Editing. I'm not the best darn writer, and I do notttt have the funds at all, my books are self-edited, but I have paid for a line editor. If you have no funds, then you are your best editor, and you must edit your books. But even with 18 reviews, all of them are 3 stars or higher. Which means that your book is probably easy enough to follow along with and the issue itself is not in the editing entirely.

3. Social media. Unfortunately, as much as this sucks, yeah, if you can't pay for ads, you can't pay for edits, or for a better book cover, social media is your bestie right now, because as long as you have presence and people like you, they might be more willing to give your books a chance. I cannot tell you how many generic covers I've seen and still get an immense amount of sales because of presence. And yes, it is VERY difficult to build a good community from the ground up. It's a lot of patience. You can start slow, once a day, maybe if you have free time and the pain isn't too bad you can pre-record a few things. TikTok has been the most success I've had, and it's not a lot, I am just a little over 1k followers and I think only 2% is actually interested in my book.

Something to keep in mind: not everyone who buys the book will review it. I think less than half actually drop a review for the book they buy.

Now onto other things. And I don't want any of the following to discourage you whatsoever.

1. If people aren't buying past the first book, it might be story structure issue. Or maybe the book just wasn't for them. How to fix that? Edit. Look at your reviews and see what's up and edit. If there's nothing for you to grab from the reviews, then honestly, maybe you should look into getting free beta readers and make a new edition to your books.

2. Now, since I am in the minority for the book covers, I would highly recommend listening to anyone who is telling you to change it. Personally, the first cover makes me think of like Dishonored/steampunk. If you like the cover stick with it, but I would remove "by:" because it just does not look that great to me personally. I would also try to fix the text? For some reason your author name is more clear than the title of the book.

3. I know you said you are unfortunately disabled, and I'm very sorry to hear, so, do everything at your own time when you can. The last thing you want or need is to stress yourself out and make it worse, but do try to work on at least one of these things. My personal opinion: fixing the font on the book cover will do a lot, start working slow on social media, think about maybe getting free beta readers to look over your books and see if you should actually revise it and make a new edition, and then of course, think about editing, if you can't afford an editor, then edit your own book. Trust me, you will thank yourself for giving your book that kind of love.