My understanding is that the "seller" refers to the general sales office at Fuse Mobius or is there a specific person I must contact ? --- Until now, I cannot confirm who is representing the Seller in this case. I have contacted a few people differently in each occasion. Each time they advised me that I can contact with one of them; namely: Khun Ae, Khon Jom and Khun Mananya. May be you can call them one day before you are going to meet them at 02-314-3377.
I assume I can sign the agreement before I have POA in my capacity as an implicit representative of my parents however the agreement will still be in my parents name? --- From my experience, there were some cases that the one who signed in the Sale and Purchase Agreement was not the parties of the Agreement.
However, if the question is "is this legally binding?", I must say that it will not be legally binding unless proved otherwise by other creditable evidence. However, as we do not have enough time to prepare the POA and have your parent send the original POA to Thailand.
I would recommend an alternative option in the event that the Seller does not allow you to sign in the Agreement as follow: once you have the Agreement signed by the Director of the Seller, you will have to scan the Agreement for my reference and have your parents sign in the Agreement and scan for my reference again prior to sending the original Agreement along with the POA for the land office and their passport.
For your information, there are two POAs for two different transactions i.e. signing the Agreement and effecting the registration at the land office.
Please let me know if you have any questions or concerns.