SolidWorks Source file included if other sizes and angles are required (or make a request in the comments).
Should print without support, there is ~0.2mm margin for the printer overprinting so the parts should fit without a need for post-processing.
The tubes can be held this way without screws or welding, but if they are loaded, think about enforcing them (maybe with cloth + epoxy glue).
The naming scheme of the exported files is as follows, let's take tubeHolder25c45.stl as examples:
25 = It's the 25x25mm tube
c = It's centered and center of both tubes touch (while e = that's on the edge of the tube and corner is always touching)
45 = means 45-degree angle, the centered tubes can be flipped and therefore I didn't provide as many angles, while with the edge ones I gave more options.