Possible downsides of plugging up small hole in foundation?
Those two holes are relieving hydraulic pressure and draining the soil outside. If you plug them, the pressure may build up and you could have water coming in somewhere else.

Is the water coming in now going into a sump? Is it wetting  the floor and causing high humidity in the "cellar"? It sounds like you might need a French drain outside the foundation to lower the water table around the foundation. But with the current situation maybe you could just fit flexible plastic hoses into the holes and conduct the water to the sump or to a drain.