I have a Samsung Galaxy Tab A.  I have downloaded epubs that I would like to sideload onto my tablet.  Even though I have the Nook app, the results are inconsistent at best.  Any suggestions?  Do I not need to download through Nook?  Is there another (better) way to do it?  I had the Kindle app and tried to download to that also (not epubs) and it froze so I deleted it.  

Are they Nook books?  If so, I'd download them via the B&N app and see what happens.

Otherwise, there is ebook software out there that allows you to read EPUBS.  I've tried FB Reader.  Seems to be okay.

i don't have that kind of a device, but i sideload epubs onto my HTC phone for reading in the Moon Reader app pretty regularly, and haven't had any problems.  there's a free version which works just fine, or a pro version with some additional features if you've tried it and liked it and plan to use it a lot.  [also, it seems to go on half-off sale frequently.]