Are you sure I know that with "Sie"(Ihnen) that is the case but in the tables "ihr" meaning you is shown uncapitalised so shouldn't "ihren" also be left in lower case?
I believe that the possesive form of ihr is --> euer. in which case, it one would want to say "your other friend", one would have to use "eueren anderen Freunden"
I think you're right. But I think the euer- form becomes euren in this case (dropping the -e- for more fluid pronunciation - or some other almost-arbitrary grammar rule that makes languages both fun and a pain in the neck!)