BUT, if you have to plumb them together. set them up so one is over the other and build an overflow from one to the other. Put the intake in the bottom one, and the return in the top one.
Ditch this idea.
Cheap-o thinking like this, will end up with water on the floor.
Just splitting intake and return will not mean both lines will flow equally.
You will end up with one tank overflowing sooner or later.
Use the 205 on the one tank and whatever on the other.