Accessing iFrame within iFrame with webdriver, JS

Simply put, for some reason the site I’m working with has set up this section of inputs as follows:

<iframe title="parentIframe">
#document (https://www.website.com)
    <!DOCTYPE html>
    <html lang="en">
        <head></head>
        <body>
            <div id="root">
                <div id="firstDiv">
                    ... //the iframes are within an arbitrary number of divs
                    <iframe title="firstChildIframe">
                        #document (https://www.website.com/subsite1)
                            <!DOCTYPE html>
                            <html lang="en">
                                <head></head>
                                <body>
                                    <input name="firstInput" />
                                </body>
                            </html>
                    </iframe>
                    ...
                </div>
                <div id="secondDiv">
                    ...
                    <iframe title="secondChildIframe">
                        #document (https://www.website.com/subsite2)
                            <!DOCTYPE html>
                            <html lang="en">
                                <head></head>
                                <body>
                                    <input name="secondInput" />
                                </body>
                            </html>
                    </iframe>
                    ...
                </div>
                <div id="thirdDiv">
                    ...
                    <iframe title="thirdChildIframe">
                        #document (https://www.website.com/subsite3)
                            <!DOCTYPE html>
                            <html lang="en">
                                <head></head>
                                <body>
                                    <input name="thirdInput" />
                                </body>
                            </html>
                    </iframe>
                    ...
                </div>
            </div>
        </body>
    </html>
</iframe>

For automated testing, we are using some fork of webdriver with nodeJS, and I have hit a wall.

I have tried using this.focusFrame() and browser.switchToFrame() with //iframe[@title="____ChildIframe"] and iframe[title="____ChildIframe"], both of which work in the Inspect/Elements search bar of Chrome, but I just can’t seem to find a way to make this work.

Once inside the parent iframe using this.focusFrame('//iframe[@title="parentIframe"]'), the runner stays frozen and doesn’t do anything, probably looking for the first iframe child on a loop and never finding it. I have no idea what I’m missing. Perhaps, since the iFrame contents are being loaded in a different site or are part of a different HTML, the runner doesn’t know what to do? What am I missing?

Thanks for your help!