Help to join

I already have a 8 gig plan for my son's phone (primary account). I want to transfer myself in from O2 onto a £20 unlimited plan and start a group plan so I can then transfer my daughter from Sky onto a £20 (£15) unlimited plan in the group and then add my son to the group.

My question is, will I get the same discounts as my primary account now is only the 8gb plan? And how do I transfer myself over from O2?

I guess there is nobody I can speak to on the phone to help facilitate this.