[BCMA] Donation dispute

[Moderated BCMA subscriber listserv.]

Seeking advice

We accepted a donation of WW1 metals from a granddaughter of the WW1combatant.  The sister of the donor has sent emails demanding we give the metals to her even threatening legal action.
>From the emails, the they to not get along. The sister didn't know the metals existed so I don't know how she found out we had just received them.
Our donation form has the line that the donor has the legal right to donate them to us. 

Any advice how to deal with the situation?  If we give them back, I believe we need to give them to the donor, not the sister.  We don't have a legal dept.

Jim Millar
Port Moody Station Museum