I know where you're coming from, dad not being in your life much, then they turn up expecting the world hun, I've had the same deal with my father.You must not blame yourself for what has happened, just because you didn't take his calls, wouldn't make him do something like that, and if it did and he is that unstable, then he needs help.
You have a lot of your own to deal with at the moment, expecting a little one and looking after your bro, so don't feel pressurized to do anything.It sounds a little harsh (and i dont wanna upset ya) but the way I think about my father is - if he could go without you for all them years, then he cant depend on you now.