Yes they will all be shiny :D, I am excited to get the Regi's shiny with my own OT, I will most likely do some 4th gen RNG captures while I wait, And you need to take out the battery manually from the Ruby/Sapphire cart or let it die , I had my Sapphire since it came out in 2003 so it died by itself :P Here is a good read on it if you are interested in attempting to try, You can't abuse your ID/SID on Pokemon Emerald so the only way to get a shiny starter on 3rd gen is Ruby/Sapphire.