is there going to be a fantastic four 3
The answer is unclear. In August 2009, it was announced that Fox plans to reboot the Fantastic Four franchise. So it looks like there will be another Fantastic Four movie, but it won't necessarily be FF3. No release date has been set.
Yes, there will be a Fantastic Four 3 and it is expected to be released in the year 2013. Read the confirmation made by Jessica Alba: http://www.slashfilm.com/jessica-alba-talks-fantastic-four-3-dark-angel-apocalypse/.
The Fantastic Four movies have included Fantastic Four and Fantastic Four; Rise of the Silver Surfer. It is not currently known if they will do a third film.