Some quick general tips, I don't know how you have your existing system set up exactly...
You can use the pathfinder behavior to find the path, together with the tile movement to do the actual movement.
Grid systems are in essence rounding to the nearest x/y on the grid, a translated coordinate system.
Set the pathfinding behavior with a cell size similar to your grid. You can then access the pathfinding node coordinates, and round/translate them to fit in your own grid system.
With the nodes in hand, you'll need to handle the movement steps manually - don't use pathfinding's move along path action. I don't believe the pathfinding can give you a node per cell, you'll have to interpolate those yourselves. Basically you need to figure out a way to describe each step between two nodes. For example, you start at 1,5 and need to go to 3,9. There's a few ways to go on a grid system. You can go right first then down, down first then right, or a mix of both by figuring out the slope.
It might be simpler for you though since it sounds like you're only taking one step at a time, so you only have to get the next step. If you have your destination node, you know if its above or below, left or right of your current position. Pick one up/down or left/right, test if there is an obstacle with tile movement's can move to position, then move. Repeat with a new pathfinding step for the next move.