Put it up to the highest level they can tolerate without being buffeted around the tank. Goldfish like some current but too much 24/7 will exhaust them.
Is there anyway you can have both filters running until you can rehome them? The higher the water turnover the better with these fish - they excrete so much mess.
Do you have anyone who can do water changes while you're away?
Will you consider removing the gravel so mess can at least be swept up into the filters? If it gets trapped in the gravel and not removed for two weeks, you'll be adding to the problem.
Is there anyway you can have both filters running until you can rehome them? The higher the water turnover the better with these fish - they excrete so much mess.
Do you have anyone who can do water changes while you're away?
Will you consider removing the gravel so mess can at least be swept up into the filters? If it gets trapped in the gravel and not removed for two weeks, you'll be adding to the problem.