Can theists be convinced by reason?

If you had said "Can believers or religious people be convinced by reason?" I would answer "No by definition" since these people are moved through the emotional faculties.

But 'theist' is a term which describes a particular point of view. I presume you're asking therefore if a theist can be made to see reason and renounce his/her view (this would assume that the theistic point of view is ultimately unsupportable and wrong) as opposed to asking whether someone could actually arrive at a theistic position through a process of reason (this is assuming that the theistic view is inherently reasonable perhaps more so than atheism).

Either way perhaps your treatment of the theists in your life is reflected back in their treatment of you. If you afforded them some measure of intelligence and be open minded to their way of seeing things then they might be willing to do the same for you.