Caution, early morning rambling brain dump to ensue ahead.
For switching, passive is fine.
For splitting instrument level signals, you need active buffers.
Otherwise, weird things happen .
Impedance mismatches, you turn one thing up, other things get quiet.
Line level signals can be split passively, but a 4 way split may be a bit much even for line level.
If doing passively, not advised, I don't see the benefit of the switch. That's a 1:2or2 splitter you have there but if it does what you need...
PPCB does have an active 1/3 splitter PC. That's cheap and easy. A 1/3 mixer as well.
Now, you don't have a 4 way splitter. Do you basically want a mono to stereo AB send and AB return? That's what it looks like in your diagram but the linked product is 1 in, 4 out. You have 1 in 2 switched out.
A few notes and questions
1)only ground you inputs and use isolated jacks for your sends to avoid ground loops.
2)do your effects that you are sending to, which I assume are stereo, require a stereo in? Or can you go mono in. Stereo out? Because that's all you are really doing anyway. Much better off either:
A) let the effects actively split the mono to stereo
B)use a buffer to drive the switch
C)use the PPCB buffer board and have an extra output available for tuner or whatever. Or don't use 3rd out.
D)use 2 active splitter boards(independent send levels), so that you only have to use 1 switch pole. Mono in-switch-splitter/splitter
E)skip the switch altogether on the send side AND use mono. So mono in-splitter board-2x mono sends(always active) and only swi5ch the returns. Assuming your pedals that are being sent to will do mono in, stereo out as previously discussed. This will work fine for non-delay/verb effects. With delay/verb, you'll get some spillover.
F)use mono in-splitter to 2 stereo (actually 2 mono pairs)but use a latching dpdt relay PPCB PCB. Switch the relay with 1 pole of your footswitch. This again saves you a pole on your switch as 5 pole footswitches arent really a thing. 5 pole toggles do exist, but pricey.
If your pedals won't do mono in stereo out but ARE diy builds, you could modify them to use a switched jack where they duplicate one input to the other input if only one side is plugged in. This is pretty common. Think when you see Left(mono)/Right inputs. The right jack is switched and duplicates the L input when nothing is plugged into the left input.
But isn't that a passive split? Why does this work okay¿? I thought you said passive was bad. Well, this is usually only done with pedals with input buffers, I e., not transistor based fuzzes, etc. if you do this with a "stereo"(dual mono) fuzz face, it's yoing to screw with the input impedance.
Hope this gives you some ideas. Don't forget about the ground loops.
Good luck
