If you have two borrowers on a residential property (not primary) and the title is being taken under a business entity (LLC) is the Mortgage to be signed only by the individuals of the LLC?

If the property will be titled in the LLC, then you need a resolution/operating agreement/etc. or what ever you usually get to determine authorized signers for the LLC to sign the mortgage/deed of trust..

Thank you. What if one of the borrowers which agreed to apply for joint credit is not in either of the corporate documents of the LLC. Would they still sign the Mortgage.

You are asking legal questions which should be asked of your legal counsel. But unless they are also vested in the property along with the LLC, an individual would not sign the mortgage/deed of trust individually, whether they are a borrower or not.

The quality of your asset depends on your ability to enforce all the terms of your notes and security instruments. Without the necessary signatures, you could end up with a total loss. These are the kinds of Q&As that can (and should) be reduced to an official procedure that's blessed by counsel.