That is a state by state thing, so ask the sitting or presiding judge for legal advise before any testimony is given.
While defendants are entitled to assert that right, there are consequences to the assertion of the Fifth Amendment in a civil action.
The Supreme Court has held that “the Fifth Amendment does not forbid adverse inferences against parties to civil actions when they refuse to testify in response to probative evidence offered against them.” Baxter v. Palmigiano, 425 U.S. 308, 318 (1976). “[A]s Mr. Justice Brandeis declared, speaking for a unanimous court in the Tod case, ‘Silence is often evidence of the most persuasive character.’” Id. at 319 (quoting United States ex rel. Bilokumsky v. Tod, 263 U.S. 149, 153-154 (1923)). “‘Failure to contest an assertion...is considered evidence of acquiescence...if it would have been natural under the circumstances to object to the assertion in question.’” Id. (quoting United States v. Hale, 422 U.S. 171, 176 (1975)).
I remember that case...
I do not know that states laws, he can maybe plead the fifth.
But ask an attorney which means ask the judge to appoint one or hire one.