My design is based on some assumptions, like your brackets are made from material as tough as ABS, separated by 20 inch to 24 inch, each spool is of 1kg, made of hard plastic, spool outer most diameter is average 8 inch & is smooth enough to roll.
I have reviewed your bracket design and done an FEA analysis with assumption of material as ABS, it is safe in stress but shows that it could soon fail by deflection/displacement over time (refer attached bracket analysis screen shot). I do not recommend reinforcement, but rather complete replacement of those brackets for safety, use 1/4 inch bolts to install brackets.
So I have designed a new bracket, currently my 3D print has 8mm wall & 20% infill, made of PLA, works great for me, but I recommend ABS with 100% infill. Besides I have used 1inch Schedule 40 PVC pipe, I recommend using 1 inch Schedule 40 steel pipe. I have added pictures of screws / bolts I have used, the design for bracket I have uploaded has hole in front to hold the front pipe in place, so that it won't roll (front pipe is just to hold funnel, so it could be of PVC, the other two should be steel)
Besides I have created a sample funnel (blue color) which could be mounted on the 3d Printer (designed for Monoprice, refer attached pictures).
Idea is very simple, you would require to design a funnel to fit on your machine (like the blue color funnel), so that it could be fed at any angle from spool, place the spool funnel (white color funnel) & fix them on the front pipe with screw (refer attached picture) in front of spool to be used, insert the filament into the slot of the spool funnel and load filament on the machine, I tried to uploaded unslotted spool funnel design, but it showed some error on the website (water tight), the slotted funnel design makes easy to remove the length of filament, yet holds it while in use. The funnel curvacture diameter is between 3 inch & 4 inch, assuming that all the material filaments could flex upto 3 inch diameter without breaking.
Hope you like the design.