Unemployment benefits are awarded through the administrative law system. In administrative law hearsay is an acceptable form of evidence, as long as there is some evidence that is not hearsay also (this is very much simplified for discussion purposes.) The Administrative Law Judge or other finder-of-fact will consider the hearsay evidence and, if s/he believes that it is reliable, will not be bound by your objections because it is hearsay.
Of course you can argue that the statements on which you were terminated are not true. That is, in large part, the purpose of the hearing. But, realistically, consider the matter from the point of view of the finder of fact. If there are three witnesses testifying to an allegation, unless each of their testimonies is built on another, that evidence will be very difficult to discount or reject as not credible. One witness who seems credible is an evidentiary problem; overcoming evidence from three witnesses whose testimonies are consistent and independent is a very long long-shot.