I do not doubt this is a wise and responsible course, to call CPS. Whether or not it will bear fruit, I don't know.
I don't necessarily trust the authorities to do the right thing, but often they do. But right now you do have communication with Kay, unpleasant as it is. This communication gives you some insight into what is happening. Your decision now is whether or not Jaden's circumstance rises to the level where CPS will intervene in a way that will help your grandson, as opposed to making a visit, and doing nothing. If this happens the communication between you will likely stop. This puts Jaden at risk too.
I think I might call my local CPS and speak with a supervisor about the situation without giving names, only to get a sense of how they would respond.
I think the right thing is to call CPS. But even right things to do can have adverse consequences. Because we do not control outcome. Just intent.