I also lost my father a couple of years before I migrated. It's a very long time ago now, but I too felt guilty about leaving my mum behind, especially as I was an only child, but that's the price you pay as an expat unfortunately. There's no easy way around it, but at least it's easier to stay in touch these days with Skype, WhatsApp, etc. My mum came out a couple of times and when she saw what life was like over here she said I'd made a good choice. If she'd been younger I'm sure she'd have moved over here too!
I'm a little surprised that you're coming over on a 491 because nearly every teacher who has posted recently has got a 190, and then been invited to apply for a 189 almost straight away. Australia is desperate for teachers at the moment, as I'm sure you're aware.