Paint Thinner (Mineral Spirits) won't do much to cured polyurethane.
The Deck Refinisher may be the silicate based stuff used in a power washer or meant to be heavily scrubbed on the surface to prepare outdoor decks and furniture for refinishing. Some have a bit of oxalic acid in them too to lighten up the wood and remove stains.
Save it for the Deck.

Lacquer Thinner may cut thru some polyurethane finishes but not others.
Of the three, this one would have the best bet to work but no guarantees .

I'd use acetone in a jar and let them soak in it.
CAreful using a common toothbrush with it as the acetone usually melts the plastic bristles and even the brush handle itself into a stick of goo. That mess can quickly end up imbedded in the wood you're trying to clean up.
The MilSpec M16 cleaning brushes that look just like a toothbrush are chem resistant and work OK with it.
The cheap wood handled w/ very fine brass wire brushes work well, or just a stiff, short bristle small paint brush.

Or use a regular commercial finish stripper and follow their directions to remove the poly finish.