You can take on the other 3 brothers as that you did Dharok in whatever order you want. What to do for the tunnels: Depending on RS gold which brother you encounter in the tunnels set your prayers for quick and most appropriate protection. If you see him, don't worry (you'll be able to survive the first couple of hits) and then, quickly fill the prayer pot and then hit the quick prayers. Make sure you finish him.
The area that consumes the majority portion of your meal is your tunnels, so be aware of the layout and get to the chest as quickly as possible. When you reach the final level, if don't have the speed to do it, take one step back from it, and hit the monster who is attacking you with an ice scream, and you'll only have 10/15 seconds to finish it.
I've gotten 62 slayer in the moment, trying to achieve 85 slayers to Abyssal Demons. I can't get on http://www.runescape.wikia.com right now, and cheap Runescape gold I want their stats while I have this free time in school to plan a set of gear, etc. for Abyssal Demons.