Step One: Does FERPA apply?
Are you or the other TAs still employed by the university? Any of you who are no longer working for the school are no longer bound by FERPA.
Step Two: Is your information an "educational record"?
FERPA links federal funding to policies governing the the release of "educational records," which are defined in the other answer.
The information the other TAs would give you does not sound like it would not be an educational record, as it is an oral account of their memory, not a record maintained by the educational institution. But if TAs normally maintain a record of the kinds of interactions we're talking about, and they consulted those records to answer your question, the answer might be different.
It's less clear whether the statement you're talking about providing would be an educational record. If neither you nor the university "maintain" the record, then it doesn't sound like it would fall within the language of the rule. So perhaps whomever you're hoping to hand it off to could draft it, hand it to you to sign, and then take it back. At that point, it's never been maintained by you or the university.
A few other notes:
If this is for a lawsuit, your statement will have virtually no value, as your hearsay account of those TA's stories would be inadmissible.
FERPA does not say that schools may not release educational records; it merely says that they are ineligible for federal funding if they have a "policy or practice" of permitting the release of educational records. So unless you are a school policymaker, you cannot violate FERPA. Of course, the school probably has nondisclosure agreements or other policies in place to ensure that educational records are not released improperly. You need to also consult those rules to determine your obligations.
FERPA is very poorly enforced by the federal government. At least as of the last time I looked at this question, no school had ever lost any funding due to a FERPA violation. Also, FERPA does not create any liability for the person who discloses the record, meaning that you could not be sued for a FERPA violation (though it's possible you could be held liable for violating some agreement with the school).