In the 2nd story bathroom, my brother was taking a shower in the shower/tub and someone noticed that there was a leak outside of the house which looks to be the same general area of the bathroom he was using. As soon as he stopped, the leaking slowed and eventually stopped.

Yesterday my sister showered in the same bathroom and there wasn't a leak. The weird thing is I showered in the master bedroom's bathroom (also on the 2nd floor around 20-30 ft away, maybe 20-30 min after she was done) and just before leaving for the day, noticed that the leak appeared again. Not sure if it was because of me or a delayed reaction from her shower?

Today I filled up a 5 gallon bucket from our downstairs bathroom and dumped it the bathroom when the leak first appeared. Did this about 5 times and no leak or signs of a leak appeared. Also used the bathtub faucet while catching the water in the bucket. Then tried the showerhead also while catching the water. Filled up the bucket maybe 2 times each and dumped it in the sink. No signs of the leak appeared.

Going to try the same in the master bedroom bathroom in a few minutes. An ideas what could be going on here? I don't really have an idea of what I should be looking for. Just trying to go through a process of elimination.

You say that the leak is outside the house. Could you please be more specific about just where this leak is?