The Fifth Amendment should be extended to any party in any type of court.
Have you read the Fifth Amendment?
No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury, except in cases arising in the land or naval forces, or in the Militia, when in actual service in time of War or public danger; nor shall any person be subject for the same offense to be twice put in jeopardy of life or limb; nor shall be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law; nor shall private property be taken for public use, without just compensation.
There is nothing in there that relates at all to third-party testimony. There is zero foundation for the position that third-party testimony be protected by an amendment that has nothing to do with third-party testimony.
If you want to make the argument that all testimony should be voluntary, you're going to have to come up with a lot better reason.