"Meantime came the guest, and knocked politely at the door." In it sould we change and into who?What"s your idea? Tanks!
It's not necessary, no. This is rather old-fashioned English, starting with "Meantime came the guest..." but it simply reads as :
In the meantime, the guest arrived and knocked on the door.
The "and" is fine. It connects two actions by the guest. He arrived. He knocked. He arrived and he knocked. He arrived and knocked.
You would only have to change it to "who" if you chose to split the sentence thus:
In the meantime, the guest, who knocked politely on the door, arrived.
Meantime, the guest, who knocked politely on the door, came.
