Are Bristlenose Pleco's and spotted Sailfin young Pleco's compatible in a 50 gallon tank? I eventually will re-home the Sailfins.

Both plecs should be perfectly fine in a tank that size, just make sure you have plenty of places for them to make their own territories and hidey-holes.

^agreed

As long as there's plenty of hidey holes they should be fine. Also don't just drop food in one spot, it's better if you distribute it more. So some in the middle, left and right. That's how I combat any aggression during feeding

agreed again with both. Kfenk has a good point about dealing with agression. follow that advice and i dont think you will have too much of an issue. I would load the tank up with heaps of wood and rock, like fill it up and that way you turn a 50gal tank into a much larger tank as far as the bottom dwellers are concerned.