What happens if 2 people fill and submit the form at the same time.

2. if i create say 5 forms to get started under the free account, how can i access all those forms offline from a single or multiple devices, and if i access from multiple devices what happens if 2 people fill in the same form and then come online and they are submited.

Whenever your form is loaded in a browser, it will be loaded as a blank form. So, two people can be filling and submitting the form at the same time, but each submission will be a separate submission, example:

Let us know if you need more help, we will be glad to assist you.

Thank you fir that, this explains as it is in a web browser, but what if I have 2 people on 2 devices updating an offline PDFs and then submit when online
Thank you
Sent from my iPad
...

It is the same. If the PDF file is located in two different devices, and the 2 people fill it and submit it, it will create two different unique submissions.

You can download the PDF file multiple times to different local drives, let say 7 PDF files in 7 different devices, and if each one is submitted, that will generate 7 unique submission.