This is civil. No fifth amendment allowed. It’s contempt of court of they refuse to answer. How much you want to bet the FBI will be in attendance?
My understanding (NOT a lawyer, just from an article I read on this - will try to find the link) is that since the FBI is investigating & there is or may be criminal liability, even though it is a civil case, there are some very case specific and fact specific issues that may result in the judge allowing some or all to plead the 5th. They cannot avoid civil liability using the 5th, but they still have their constitutional right to avoid criminal liability.
More info on taking the 5th in a civil matter:
http://apps.americanbar.org/buslaw/blt/blt00may-shield.html
Excerpts:
The Fifth Amendment to the Constitution actually says:
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 offence 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.
(Emphasis added.) Because the privilege “can be asserted in any proceeding, civil or criminal, administrative or judicial, investigatory or adjudicatory,” Kastigar v. United States, 406 U.S. 441, 445 (1972), the lawyer who has not navigated these particular legal waters before — and this may include most of those practicing in the civil arena — may fear (or trust) that the very invocation of the privilege will foreclose all further questioning, on any subject.
Civil cases are different. In civil actions, however, there is no prosecutor on hand. The issue then shifts to whether “the claimant is confronted by substantial and ‘real,’ and not merely trifling or imaginary, hazards of incrimination.” Marchetti v. United States , 390 U.S. 39, 453, 88 S. Ct.. 697, 705, 19 L. Ed. 2d 889 (1968). Because the privilege against self-incrimination applies only in “instances where the witness has reasonable cause to apprehend danger” of criminal liability, the deposing lawyer should assess in advance, in light of what counsel knows about the case, whether the witness has a realistic basis for such a fear. Hoffman v. United States, 341 U.S. 479, 486, (1951), quoted in U.S. v. Argomaniz, 925 F. 2d 1349 (11th Cir. 1991).