That is incredibly easy. Sorry I didn’t know you meant this, I thought it was more complicated 
So just place two texture samples in a material. Then place a “linear interpolate” node. You can simply press the “l” key and click anywhere.
Then hook up your two textures into the A and B slot.
Then create a scalar parameter. To do this hold “s” and click and give it a name, maybe something like “alpha” or “blend”.
Then you can change the value of that scalar to blend between the A and B inputs. This doesn’t just work for textures, it works for blending any set of material nodes.
You can control the blend either in the base material, or by creating a material instance to be able to drag the value using a slider. Or you can use a blueprint to create an MID and change the value during the game using the set scalar parameter node on the MID.