Try putting just one cup on, hook the single tube directly to the pump. Then do the other one. If one stays on and the other one doesn't you have narrowed down the problem.
Does that lose pressure slowly or does it not grip at all?
Yes, 5 is probably minimum. But be careful at 12 you could be doing some damage, look out for blisters, bruises, sudden large expansion, little red dots and even steam in the domes. Any of these and you are too high.
I know women have reported better results when they pumped twice a day instead of one longer session, so I think it is a good idea to try. Make sure you also massage with oil, recommend coconut or almond.