Is there a legal contract or form I can use to allow another couple to stay in my apartment temporally without being on the lease or without the landlords knowledge or consent?
If your lease with your landlord forbids subletting, then no form will be sufficient. If not, then what you seek is a subtenency agreement. Just about any attorney can draw one up for you. You may find fill-in-the-blank forms in stores or on the net, but I do not reccomend any of them.
Good luck