The phrase "are not yet fixed" is correct and usable in written English.
It can be used to indicate that something has not been determined or established at the present time.
Example: "The details of the event are not yet fixed, so please check back later for updates."
Alternatives: "have not been finalized" or "are still undecided".
The euro is still young and the euro zone's borders are not yet fixed.
Price and delivery date (both for Japan and a possible overseas version) are not yet fixed.
But if Leicester are to capitalise on this season's success and cement a permanent place in the hearts of Thai football fans, its owner is going to have to invest more in raising the profile among younger supporters, whose loyalties are not yet fixed.
Prices for games to be sold outside Japan are not yet fixed, but keep in mind the retail prices listed up above are usually undercut by 10-15% (especially by big Japanese electronics discounters) once the games are actually ready to hit stores.
In LSDs, we detect those duplicate genes still in this state of flux as they are not yet fixed in the population.
The prices of the generic drugs are not yet fixed, and may decrease over time, with higher volumes and competition between generic companies.
The roof, to pick on George Osborne's phrase, is not yet fixed and he will need a full five years of sunshine to finish the job.
To the degree that a museum of modern art implies a dedication to art whose history is not yet fixed, or fully fixed, any attempt to articulate a cohesive and concise narrative about such work is more likely to be provisional than definitive.
When she is writing historical fiction, she knows what will happen and can do nothing about it, but she must try to imagine the events as if the outcome were not yet fixed, from the perspective of the characters, who are moving forward in ignorance.
