Question about how to combine psbt

I have a question about psbt. If you want to combine two psbts, one will be signed with Alice’s private key and the other will be unsigned. Now we want to take the input and output of the signed one, combine the unsigned psbt, then build a new unsigned psbt, then sign it with two different private keys and finally broadcast it to the Bitcoin network. So I would like to ask: Is it possible to combine two psbts (one signed and the other unsigned)? If anyone knows anything about this question, could you please post relevant examples or code here? 🙂 thank you.