I wonder if Kodak's instant was a joint venture, or if Fuji bought some of Kodak's IP, from the Kodak instant program.
Kodak developed the technology, incorporating everything necessary to avoid patent litigation from Polaroid.
Polaroid sued anyways, and the trial judge came to a decision against Kodak that fundamentally increased the protection offered by US patents to something that had never been known previously in US patent law.
The decision was probably a major factor in the eventual bankruptcy of Kodak.
In the meantime, Fuji developed Instax technology that essentially encroached in the same way on the Polaroid patent, but Polaroid didn't sue them.
Edwin Land rejected a settlement of the Kodak litigation that had been worked out by the respective lawyers, and which was consistent with the then current situation in US patent law. By that time, there was a fair amount of animus felt by him against Kodak - ironic really given that he had had to rely on Kodak to supply and manufacture significant amounts of Polaroid materials over the years.
Polaroid of course also subsequently went bankrupt, and Fuji just kept working on the same technology that Kodak got sued for.