I don't think it is semantically correct to include radio buttons in a list, which is I think what causes the unexpected behavior. If you try it with markup like this, legend
is read in Chrome and Firefox:
<fieldset>
<legend>Do you like boats?</legend>
<input type="radio" id="boats-y" name="boats">
<label for="boats-y">Yes</label><br />
<input type="radio" id="boats-n" name="boats">
<label for="boats-n">No</label>
</fieldset>
Would you like a PR with this change and updated readouts for Chrome and Firefox? I can also provide updated readouts for VoiceOver Chrome/Firefox/Safari and NVDA Chrome/Firefox/Edge, but I don't have access to JAWS to help with those.