you dont team magma is on your side(they are not the bad guys team aqua is)
No, you cannot be a member of Team Aqua / Team Magma in Sapphire.
There is no magma amulet in ruby. The location in which team magma's hideout is actually is the place where team aqua's hideout is in sapphire and emerald (i think you confused sapphire with emerald)
The Magma Base doesn't exist in Sapphire Version, but the team Aqua's Base is located outside of Lilycove City.
Team Magma is absent in Pokemon sapphire, but exists in ruby. Same with team aqua in ruby version, both teams only coexist in Pokemon emerald version
they will be on the montain, once you have obtained the magma badge
your get from team aqua or team magma i think
team aqua and team magma, u have to beat them both as opposed to ruby and Sapphire where u only have to beat the team that is the same color of your game(ruby=magma)(Sapphire=aqua)
Get the Goundon
there is a cave north in the water. go in there and defeat team aqua.
Google Pokemon sapphire walkthrough and search through a walkthrough
U go to the magma hideout and defeat Maxie
i don't exactly know because i don't play Pokemon ruby sapphire and emerald i only play Pokemon games for the ''ds'' like Pokemon black and white not for ''game boy advance'' like Pokemon ruby sapphire and emerald