Ownership rights, or whether it is permissible to use other people's models.

Hello. I have a somewhat unusual question, and it might be off-topic. I want to transfer the world of Heroes into a real-time mode. To do this, I'm creating a mod for The Lord of the Rings: The Battle for Middle-earth 2. I'm taking models from Heroes 5: Tribes of the East. I want to immediately introduce factions like: Sanctuary, Fortress (Swamp), and Conflux. To do this, I need models from the corresponding mods. Also, I need some units from the NFC project and models of some heroes. I'm not claiming authorship; I'll have to make some minor edits, at least for rigging. Question: who do I need to ask, and do I need to ask permission to use these models? P.S.: Many of the models belong to the user psatkha, and he often visits this forum, so I'm asking here.