Please do yourself a favor and consult with an attorney. I am an IP attorney, but I handle patents and trademarks, and I refer copyright issues to other attorneys, as the area is extremely complicated. Regarding the term/expiration of the original work, it depends on several factors such as when/if the first work was published or registered. It will also depend on if the Copyright was renewed. You may be able to look this up online at the Library of Congress, but this may not be straightforward. None of this is legal advice, and was copied/pasted from the link provided above:
Federal standards for copyright duration differ substantially
under the 1909 act compared with the 1976 act because
of the renewal term contained in the 1909 act. Under the
1909 act, federal copyright was secured on the date a work
was published or, for unpublished works, on the date of
registration. A copyright lasted for a first term of 28 years
from the date it was secured. The copyright was eligible
for renewal during the final, that is, 28th year, of the first
term. If renewed, the copyright was extended for a second,
or renewal, term of 28 years. If it was not renewed, the
copyright expired at the end of the first 28-year term, and
the work is no longer protected by copyright. The term of
copyright for works published with a year date in the notice
that is earlier than the actual date of publication is computed
from the year date in the copyright notice.
The 1976 Copyright Act carried over the system in the
1909 Copyright Act for computing copyright duration for
works protected by federal statute before January 1, 1978,
with one major change: the length of the renewal term was
increased to 47 years. The 1998 Copyright Term Extension
Act increased the renewal term another 20 years to 67
years. Thus the maximum total term of copyright protection
for works already protected by January 1, 1978, has
been increased from 56 years (a first term of 28 years plus a
renewal term of 28 years) to 95 years (a first term of 28 years
plus a renewal term of 67 years). Applying these standards, all
works published in the United States before January 1, 1923,
are in the public domain.
