Can we use assets others have made, assuming we have the license? Must all assets be made inside the jam window?
Assets that are made outside the jam by you or your team is not allowed. Let me get that clear. If you have ready-made assets and you have the license to use them, you can use them. It's perfectly fine if your game consists of only art made by others. It is allowed.
If you have more queries, please reply here or consider joining my discord server and asking your doubts in the #questions channel.