It should not stop when another play enters. And generally you should hardly ever be getting pked. Do you have wildy hard diaries done?
Could you send over the logs from a session which stopped early please?
You can do just blood barrage like this:
EDIT: actually you can set the "Loadout Blood Spell" to none. I think if you set it as both it will take more runes
This is a common issue people have with Spindel, as it is the only one where Stamina/Super energy pots are required.
Make sure you start with some of those in your inv