Thanks for your question and good afternoon.
You would need a trust lawyer here to file a civil suit to challenge the trust.You would be claiming lack of capacity, and other grounds.You woudl have the burden to have the courts review the trust and his mental capacity at time he made the trust.
You may want to go on and locate a lawyer here so that he may gather affidavits or statements that support such a challenge.One of the problems with such a legal challenge is that over time people decease, relocate, or their memories fade, etc.The lawyer can seek to do this while he is alive and then discuss when to file your civil suit to set the trust aside.
It is possible to have a civil suit to declare the trust invalid but you will need a lawyer to do so as well as gathering evidence to support your suit here.
Here is the law pertaining to such suits and the time limits to file.
58a-604: Limitation on action contesting validity of revocable trust; distribution of trust property. (a) A person may commence a judicial proceeding to contest the validity of a trust that was revocable at the settlor's death within the earlier of:
(1) One year after the settlor's death; or
(2) four months after the trustee sent the person a copy of the trust instrument and a notice informing the person of the trust's existence, of the trustee's name and address, and of the time allowed for commencing a proceeding.
(b) Upon the death of the settlor of a trust that was revocable at the settlor's death, the trustee may proceed to distribute the trust property in accordance with the terms of the trust. The trustee is not subject to liability for doing so unless:
(1) The trustee knows of a pending judicial proceeding contesting the validity of the trust; or
(2) a potential contestant has notified the trustee of a possible judicial proceeding to contest the trust and a judicial proceeding is commenced within 60 days after the contestant sent the notification.
(c) A beneficiary of a trust that is determined to have been invalid is liable to return any distribution received.
It has been my pleasure to assist you today.Please let me know if you have more follow up.Thanks again.