How would multiple people send in one transaction? Is it possible to have multiple inputs, from different people?

How would this be set up?
Is it possible to have multiple inputs, from different people?


the bitcoin system doesn't know people - it is working with transactions, that move funds from address to address. Still the answer is "yes". You can create transactions, that spend funds from different addresses. To be more specific, we would talk about UTXO, but I think that goes beyond scope of the question, and the developers webpages have enough explanation (see reference below).
Exchanges create such transactions all the time, or also faucets. They (can) have multiple inputs, and multiple outputs as well. 


  How would this be set up?


you would follow the specification :-)
A guided example is in  the Complex Raw Transaction section of the developer examples.