The easiest way is to do it as in reality. You have to draw the main tube via a sketch on a plan and put the Diam of the tube at the end and make a boss/base swept in the 1st part then create a second part and make a 3d sketch with the direction to take and at the end again create a plan to put the Diam of the tube and redo a boss/base swept then create the assembly. In this one you can remove material at the junction of the tubes and propagate the function to the parts. You should be able to do it if you know a little bit about Solidworks.
I think that for the first profile, a smoothed boss/base is the best solution as long as you have a reduction on it (if you ignore this reduction you can do a brushed boss/base). For the other two profiles, you can work with a 3D sketch and make another one a brushed boss/base, or you can create new plans and sketches for the directions.