I think you need to be really honest with yourself about what you hope to gain by telling your parents. You can work on enhancing your boundaries without revealing anything to them. I wonder if part of the appeal of telling them hides the hope that doing so will relieve you of the burden of enacting boundaries for yourself. I don't believe in general that telling them necessarily will make it easier to enact boundaries, and it could actually backfire.

I'd also consider their age: if they are in their 50's-60's, there's probably more possibility of forging a different future relationship with them. If they are elderly, you really have to ask yourself what you hope to gain, and at what cost to both of you.

I'd also want a very clear explanation from your T of her thinking on this.