An sqs file is just a text file written in a format that OFP recognizes. It can be edited with windows notepad. You can just copy and paste code from one script to the other. Of course, the code may clash.
EDIT: Or maybe you're asking how to execute two separate scripts at once. In that case, all you've got to do is put two
exec commands, one after the other, separated by semicolons, in an initialization, trigger "on activation" field, or other executed script. Example:
[group this, leader group this] exec "stand.sqs"; [parameters] exec "hold.sqs"
Where parameters is the appropriate parameters for hold.sqs. Without knowing what the script is I don't know what those are.