Hi Luke,  If for some reason you siblings have a strong sentimental
attachment to this particular piano, then to them it could be
"priceless" as a family heirloom and nothing will dissuade them from
their belief(s).

If, however, they perceive the piano as a "valuable item that could be
sold for a profit" (and inasmuch as you're presumably "sick of it" with
the piano -- and them) then I'd suggest you most graciously give the
piano to your siblings for free.  (They, of course, will move it or pay
to have it moved.)

Or else sell it to them formally for $1.00, with a receipt documenting
that the sale is made "As Is" and the buyer(s) have been made aware
that expected repair and/or restoration is likely to cost more than the
re-sale value of the piano once fully restored.

After that you should have a clear conscience if your siblings accept
or buy the piano and then throw money at it being restored.   The same
holds true if you told your siblings not to touch the stove, because
it was hot, and then they went and got burned -- it's not your problem!

My Granddad used to say, "A fool and his money are soon parted."
He also said, "The smart man/woman learns from their own mistakes, the
_wise_ man/woman learns from the mistakes of others."

Apparently your siblings are neither smart nor wise and perhaps are
un-heedfully foolish.

Best of luck!

Don Caine - The Music Box Repair Center Unlimited
Lomita, California
http://www.musicboxrepaircenter.com/