tixati_portable_mode.txt
tixati_standalone_mode.txt
tixati_local_instance_check.txt

1. Are all these independent of each other or can they be combined in some way?

2. If they can be combined, how?

3. If they're independent and more than one is present, what will be their order of priority? (That is, which one will override the other?)

4. If it is desired to have everything as self-contained as possible, so that each copy can be carried around and also not interfere with any other running instances (either installed or portable/standalone), will the presence of tixati_local_instance_check.txt alone suffice?

No-one has a clue about these except the developer?

@Janet?

Tixati_portable_mode.txt and tixati_local_instance_check.txt work fine together/combined. Haven't had use for tixati_standalone_mode.txt, so I can't say for sure, but as it's a variant of tixati_portable_mode.txt, it should work with tixati_local_instance_check.txt, but probably not with tixati_portable_mode.txt.

According to me tixati_local_instance_check.txt doesn't need any of the others to function. Can someone else confirm?

I can confirm this. if you have just the tixati_local_instance_check.txt file and the tixati file you can run the program.