Could tI- be read, "yourselves?"
No. The prefix tI- refers to a group of multiple third person objects and "yourselves" would be second person. The only way to do that would be with the -'egh suffix as is shown in this sentence.
Yes. So, tIHub'eghrup ?
No, that is not possible -- you wrote "Be prepared to defend yourselves them!"
So you have two objects: "yourselves" (from the -'egh) and "them" (from the tI-) and the result simply makes no sense at all.