How to attach multiple circuits to same connector?

[Piotr]

@kevinz

If my question isn’t clear,

I understand that you used at schematic and PCB 3 connectors having 8 pins each and you ask how to replace them wit 8 connectors having 3 pins each.

It is how I understand this:

@kevinz

connection to each circuit is to just a part of a single connector?

The answer is: start from using 3 pin connector symbols. Use 8 of them at schematic, make there wire connections and there should be no problem to map it at PCB.
If you ask how to clearly make these connections at schematic my recent post can be helpful:

First prototype PCB. Any tips or pointers? (arduino giga hat)

When connecting microcontroller to bus I place wires from each pin to bus then deciding what is connected where I just manipulate with labels. Unused pins are left with unconnected wires and I don’t remember ERC complaining on it. Ops… got an idea that I may be permanently switched off some warnings. Down to 0603 you can relatively easy hand solder having soldering iron with sharp tip. If it were my schematic the I2C connectors would look something like that: [I2C] And only one line (bus) …