I think that you are trying to describe a three switch box where a black hot feeds three switches. All of the blacks are connected together, perhaps by a wrap around one screw and then connected to the next switch.
In any event, you can daisy-chain the blacks by connecting the incoming hot to the Line on the Inovelli and then connecting a jumper to the next switch by using the other Line hole on the Inovelli.
If this isn’t what you’re describing, please post back.
If you use two different size wires in the holes (referring to your original question) I’ve noticed the smaller wire is sometimes not held tight. So if you use a #12 and a #14 double check both are firmly gripped. If 2 #14’s you should be OK.