If your mum doesn't normally make everything about her, then I'd say she's probably still processing, hopefully she can be more supportive and understanding in time. I'm sorry about your step dad too. My advice would be to stick to asking about the genetic stuff, the information that could be useful to you now, who your grandparents are etc, maybe save the emotional stuff for when you get to know him. I say that just to be careful he doesn't let you down again. This is big exciting news though. Best of luck:)