Clearing Firmware Lock - 2016 Macbook Pro (UK)

I'm in the UK and I have a 2016 Macbook Pro. It was my dad's. He died 2 weeks ago.

I have proof of purchase - the original receipt in the box.

I tried to factory reset it, because it's clogged up with all kinds of stuff and isn't running well, but I wasn't able to because I was confronted with a firmware lock screen which seems to want a password (which I don't have, unfortunately).

Will my local Apple Store (probably the one in Westfield Stratford in London) be able to clear the firmware lock for me if I take the proof of purchase with me? I'm not the purchaser of course, but I do have my dad's death certificate if they need additional evidence that I am who I claim to be.

If they can do it, will they charge a fee?

Thank you.