The only thing there that could possibly be explosive is the propane, and those tanks in practice can only explode if you literally throw them into a fire. You can leave those things baking in the sun and they will not be dangerous. I know from experience. AZ heat won't phase them, and on the off chance it ever does over pressure because it was incorrectly filled, there is a relief valve that vents the gas up and away from the tank. Without an open flame right next to it, the gas will harmlessly vent off. I don't see anything there that you need to be concerned about if this is merely about safety.
If you are really concerned, just tell your family politely and discretely to please not smoke near that area. I don't think it needs more than that if you don't care about their actual purpose.
The only thing there that could possibly be explosive is the propane, and those tanks in practice can only explode if you literally throw them into a fire. You can leave those things baking in the sun and they will not be dangerous. I know from experience. AZ heat won't phase them, and on the off chance it ever does over pressure because it was incorrectly filled, there is a relief valve that vents the gas up and away from the tank. Without an open flame right next to it, the gas will harmlessly vent off. I don't see anything there that you need to be concerned about if this is merely about safety.
If you are really concerned, just tell your family politely and discretely to please not smoke near that area. I don't think it needs more than that if you don't care about their actual purpose.