Not sure what you mean by "flat". If you mean under inflated, then that is normal. Tires lose 1-2 psi per day. After a month, your tires will be significantly under inflated and you'll want to top off before riding. Try inflating the tires to spec on both bikes and check back in a day or two. In that short a period, you'll know if you have a puncture or not. FWIW, it would be unusual for both of you to have punctures in both of your tires from your last ride...
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No. There should still be air in the tires. You probably have a puncture.
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