My local Atlas agent has asked me to sign the moving cost estimate along with two additional documents which are titled "Order For Service" and "Value Declaration," but I don't want to sign these documents until I am certain that the sale of my house goes through without any problems. What are these documents and why do I have to sign them? If I do sign them what are my obligations to the mover? Please help.

Thank you for your question!
The documents you have been asked to sign are not contracts. These documents are mandated by federal consumer protection laws and, in a nutshell, provide the customer with written confirmation of the arrangements you have made with your moving company, including (but not limited to )...
Signing these documents does not obligate you to utilize the mover and, once again, these documents are for your protection. You may sign them without any worries.
You can read more about this subject by reading the federally mandated publication, "Your Rights and Responsibilities When You Move."
Thanks again for your excellent question and stay well.