My fried lives in Stuttgart, and I live in a small village called Isny im Allgäu. We are planning to travel to Konstanz together. The problem is that there is no train in my village, so I need to take two buses to reach Ravensburg city. I can wait for him to get in the train with him.
The question is while he's coming from Stuttgart, can I use the ticket which is already for two passengers to get to Ravensburg city, because the train goes from Stuttgart to Friedrichshafen through Ravensburg?
I'm not sure if I get your question right. Are you planning on both using the same ticket at the same time, but in different busses/trains? That does not work.
You should not have any issues using the ticket with less people then it is for (i.e., traveling alone on a two-person ticket). However, if you want two people to use the ticket, they have to travel together.
No.
I think you are confusing two things: A bus ticket is completely different from a train ticket. There are in fact train tickets which allow for an extra fare to use the bus tickets in the destination area (z.B. SchönerTagTicket NRW), but I take an educated guess that Ravensburg as middle station is out of reach.
Please also state exactly what kind of ticket(s) do you have because there are many special tickets so your question is currently unanswerable.