Generally speaking, when a trust is sued, the trustee may use trust funds to defend the lawsuit—even when the trustee is sued. Litigation can be expensive, and as the trustee, you have the authority and discretion to advance the cost of legal assistance from the trust. Of course, the hope would be that the money advanced for legal fees would eventually be recovered during litigation.
If you are found to have engaged in negligence or misconduct, reimbursement for legal fees could be denied.