Hi Massima
great questions.
1. In FGMEMBERs you do not need permission to submit patches via pull requests (no aircraft "ownership" in the strictest sense). Feel free to fork any plane, add the livery and send the pull request... any time, any craft.
2. If you become a "member", you can even accept your pull request yourself; since you will be granted push access to all our repos
[This may differ in the Aircraft is in the NONGPL area, and it is cover under NO DERIVATIVE licenses]
3. More in topic with your questions:
a. Is it possible to upload the livery without permission of the creator? (FGMEMBERS/FG DATABASE/or even other)
The answer is: Do you have a license to do so? Example:
If the livery comes with no explicit answer, then the most safe position is DO NOT. Lack of a license, means exactly that there is not explicit permission to do so.
GPL license, gives you the license to copy/modify/redistribute. So if the livery is under GPL that means, yes you have the permission (also known in legal terms as "license".
It is not safe to assume something is GPL. So, when in doubt, ask.
Can you contact the author of the liveries (email, contact form, other) and ask him if the liveries are GPL covered? or if they are not, what is their limitations on redistributions (other license? etc).
Keep in mind also
1. All liveries in the FG database are GPLed
2. Although "doable"; It is cleaner and safer
not to upload not GPLed liveries in GPL aircraft, even in FGMEMBERS. To prevent the licensing of the aircraft to become a mess.
b Can a livery be redistributed without a license?
Really: Not. Unlicensed material is more broadly covered under "ALL RIGHT RESERVED" clauses, which state that copying and redistribution (let alone modifying) is all restricted to the owner/creator/copyright holder. It falls into the absurd realm that actually holding a copy of the file in your hard-drive already fell in the copy realm, and thus, you may not even have permission to do so. Copyright laws trend to be asinine.
Again, going back to the previous answer is: Contact the author. Ask if the material is GPL. Long chances exist that it actually IS GPL. Just the author forgot to explicit that fact.
If we gave everybody in the World free software today, but we failed to teach them about the four freedoms, five years from now, would they still have it? Probably not, because if they don’t recognise their freedoms, they’ll let their freedoms fall