1, Is that possible to update my F3 to F5 same lifetime and 5 users?
No, permanent licenses includes 1 install per license you purchase. Only a Object desktop subscription includes 5 installs at once.
2, Is that possible, I only update, or occupy one or two activations from F3, and got corresponding one or two activations for F5. By doing so I can have some discount.
An upgrade is just another word for a discounted price. You will always keep your 5 installs of Fences 3 no matter how you purchase Fences 5. So if you upgrade to a 1 year subscription you will still keep all your fences 3 installs.
3, My 1 and 2 question cannot be done, the only way is to buy a brand new F5 for one user, and then I have 5 key for Fenses3 like before and that the same time I have one extra Fenses5?
Yes, and if you want a permanent lifetime license this would be the only way to do it