Do they really want me, or is it just their job? I hear they're v overworked ATM.
Yes we want good, hard-working students. But pleeeeeeeeese, if you're going to do a PhD, do it. Try to have some commitment & confidence that you can do it. Blips in confidence are normal, but please don't visit constant anxiety on your supervisor.
I have a mature-age student who is anxious and under-confident. That is what is hard in supervising them: I have to spend my emotional energy & about half the time in each supervision, reassuring, persuading and cajoling.
I am getting to the point where I may just challenge them: if you think this is so bad and you're not worthy or capable, just stop doing it.
If a supervisory team is interested in your topic, and willing to take you on, and can see potential in your proposal, go for it.
Or not.
But make a clear decision, and if you go for it, then take your supervisors' advice about the potential of the topic, and your ability.
A PhD won't necessarily get you an academic job nowadays, so at your age & career stage, be prepared for going back to your current profession. Or a version of it.