PCB analog and digital split impossible with multiplexers?
Series resistors:

They are series termination resistors, close to the source of the signal. They won't reduce the data rate of your signal, will just make their rise/fall time longer (slower edges).

There are some quick references to this by Henry Ott, and this video by Robert Feranec, and some detailed explanation in this EE.SE question/answers, so I won't go into too much detail.

But basically, the faster your signal changes on a line, more noise its gonna induce around it.

Resistor arrays:

I like YC164, which are easy-ish to hand solder or place manually on pasted PCBs. But basically they are a space saving and "part count reducer" if you are soldering stuff by hand.







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