Warning (Restriction) is interfering with the submission of grammatically correct keywords

@bradley_kent​ 

You used a non-standard apostrophe. Perhaps the form ought to be able to automatically adjust those characters.

Since it isn't recent that the slash character is not allowed, keywords without it are already used, such as september-11-2001, reference-to-9-11.

There is only one apostrophe on my keyboard.  How is it 
"non-standard”?

There is one apostrophe on every keyboard, but there is more than one computer data character for the same concept of the apostrophe, and some software picks one of the non-standard apostrophe over the standard apostrophe.

The examples contain U+2019 ’ RIGHT SINGLE QUOTATION MARK and not U+0027 ' APOSTROPHE.

If I type 'hello' in this text box I get apostrophe but...

If I type ‘hello’ in Apple Notes I get U+2018 ‘ LEFT SINGLE QUOTATION MARK and U+2019 ’ RIGHT SINGLE QUOTATION MARK. Copy and paste and they end up in this text box.

Same keystroke, three different outcomes. That sort of behaviour is common in word processors and text editors not intended for use in technical contexts. IIRC Microsoft described that behaviour as "smart quotes" when they introduced it many years ago.

@bradley_kent​ 

You may wish to use the existing brother accidentally kills his brother, if it applies.

Doesn’t apply in this specific case since it is NOT a brother accidentally killing his own brother, BUT someone else accidentally killing someone’s brother.

What about:

fighing-for-one’s-life

????

Guess that can no longer be a keyword because it includes an apostrophe. Oh, well... "fighting- for-one’s-life," in IMDb's eye, is apparently not important and should be declined.    The generalized “fighting-for-a-life: or  “fighting-for-life,” I suppose, are acceptable, but they do not accurately communicate nor factually represent the exact situation.

@bradley_kent​ 

accidental-killing-of-one's-brother would suggest to me that the person killed is the brother of a person causing his death.

You need to use the standard apostrophe that has been posted in this thread and is included in the error message. You can also copy the keyword from the keyword search, fighting for one's life

@bradley_kent 

Just replace "accidental-killing-of-one’s-brother" with "accidental-killing-of-one's-brother" and it will work. If you zoom in on those keywords, note that the apostrophe in the first one (the one that gets rejected) is slightly curved, while the apostrophe in the second one is straight. The first one is the "non-standard" apostrophe mentioned by @Peter_pbn. 

On a more substantive note, some better keywords than "accidental-killing-of-one's-brother" would be accidental killing, brother kills his brother, and brother accidentally kills his brother, if it applies (as mentioned by @Peter_pbn).

The problem with "accidental-killing-of-one's-brother" is that it's in the passive voice and in gerund form, rather than in pure noun form or active verb form, both of which are more commonly used as keyword forms and therefore preferred. For example, does "accidental-killing-of-one's-brother" mean that a sibling killed their own brother, or that someone else killed the brother in front of the sibling? 

Even "accidentally-killing-one's-brother" would be better, because at least the reader would be able to tell at a glance that the brother's sibling is the person who did the killing.