Edict of Milan/Constantinte

I am troubled. Tell me if I got any facts wrong here.
Galerius Maximius did not like the fact that Constantanius assigned his son, Constantine, to become the next Augustus following his death at 306.

Did Galerius refuse to ackowledge Constantine's title as Augustus, or was Galerius so powerful at the time that he only allowed Constantine to have the title of Caesar only? Why would Galerius have the power, was he an emperor above all? What was his relation to Diocletian and the Tetrarchy? It looked like Constantinus was a result of him falling in power. Weren't their 6 emperors at the time? (What about their other titles, di they believe they were 'sole' emperors?)

So some fighting is going around, and all of a sudden Galerius feels like issuing the "Edict of Milan" (311) to stop persecuting Christians, and before that he was a big time Christian Persecutor.
Then Constantine in 313 created the "Edict of Toleration" after his vision in 312.
This leads me to believe that the Edict of Milan never existed or Galerius had some political motivation that I have not been able to find out.

Was Constantine's mother a Christian her whole life, is her story floating around anywhere? I know what she did, but I don't know how she became a Christian. I believe she was one before her son.