I hope this message finds you well. I am a licensed attorney with over a dozen years of experience handling matters of this nature. It is a pleasure to assist you today.
As co-trustee, you have equal rights in the administration of the trust left by the deceased to your other trustee. So, first things first, you need a copy of the trust if you do not already have one. Read it through and make sure you understand what the deceased desired at the time the trust was executed.
Since the deceased's son is the other trustee, the path of least resistance here in my experience is to let him "guide the ship" so to speak as long as he is not running afoul of the mandates within the trust. In short, you keep him in check by being silent but observing. Ask that he keep you in the loop with all trust decisions.
If he is not keeping you in the loop or if he is running afoul of the trust mandates, you can then make a decision as to whether to bring this to a courts attention. Otherwise, you sit and monitor under the circumstances.
Let me know if you have any other questions or comments. Please also rate my answer positively (THREE OR MORE STARS) on the rating bar on your end so I will receive credit for my answer.
Thank you and best wishes going forward!