"Temporary use for lawful sporting purposes" means the gun's owner from state A can hand a gun to someone from state B when both of them are out hunting or target shooting or something, without there being an illegal transfer. It does not mean that someone from state A can ship a gun to someone from state B. A good simple test is "can he hand the gun back to me?" If yes, it's probably not an illegal transfer. If no, then it almost certainly is.
Some states do not allow private transfers between residents of that state, but make exceptions for transfers between family members (who are residents of that state). This has nothing to do with inter-state transfers. Federal law does not make any exceptions to transfer requirements due to familial relations.