NOT VALID FOR REENTRY TO U.S. is a generic message printed on all EAD cards that are not issued with i485 filing.
When you apply for i485 pending EAD card + AP (Advance parole), you can use that EAD+ AP card to re-enter US.
In your case, you have L2 EAD which cannot be used to enter US. Instead, you need to use your L2 visa stamp.
Don’t worry, it really does not mean anything for you as you will use your visa stamp for entry.
You can travel with anyone you like. There are no restrictions.