I would start the first tank in the far corner of the second picture. Extend it out all the way along the banister so you don't need to extend an extra two feet. For the banister, I would take the top moulding piece off, take off the 2x4 underneath to check for any weird wiring that would extend to the top of that banister. If there is nothing, I would lower the height of that banister with a good reciprocating saw to the stand height of the tanks. Then put on a 2x4, put the moulding back on, trim up the edges with estra moulding. Yes you will still have a banister there but it won't obstruct your view of the tanks and you won't need to add 2 feet to that banister. Before you put the banister back together, you can even plumb into the wall and down between the joists and into the area you choose to have your sump.
Or just sell the two 180's and use that money to custom make a tank that is the length of that banister.
