My understanding is that technically, no, it's not "hearsay", because they heard it directly and not from a third party.
It is also apparently admissible in Florida law.
But it should be discredited by the testimony of a friend of Terri who says that MS told her repeatedly that he did not know what Terri wanted him to do.
That negates MS testimony and the testimony of sis and bro in law are not really relevant because they are only in support of MS claim.
The basic problem is : hell bent on death Greer chose to believe what he wanted,and disregard everything else.