[fifo][1]s are not for saving or reading more than once. You may find [tee][2] better suited to your goals.

Untested guess at what you want:

    mkfifo myfifo1 myfifo2 && curl -s http://192.168.1.27:8554 | tee myfifo1 > myfifo2;

Then read the 2 files with vlc and omxplayer, or do the things with the now duplicated data stream.

Note that you can set the fps on raspivid and with it's temporal compression it may be better than looping raspistill in some conditions. 


  [1]: https://en.wikipedia.org/wiki/FIFO
  [2]: http://unixhelp.ed.ac.uk/CGI/man-cgi?tee