Important ventilation question for my grow tents.

I am a first timer and have some questions about my ventilation setup. First thing let me explain my setup so you know the situation.
I Have The secret Jardin Dark TwinII with the a grow panel 14 watt led up top and a 90 watt UFO led in larger bottom tent. 4 home made deep water culture setups in the top and a five gallon bucket deep water culture in the bottom.I have a four inch intake fan drawing air into the bottom tent the exhaust from the larger tent is ducted into the intake port on the top tent. On the exhaust port for the top tent I have another four inch fan for exhaust hooked to a Phresh filter so the ventilation system for both tents are shared. Finally for my questions.
1. Will sharing my ventilation between smaller "mother" tent and my bottom grow tent cause any problems? (hermaphrodites etc.)
2. How do I block Light form coming through my ventilation tube between two tents?(both are on a vegetative cycle now but later one will flower while the other stays on veg.)
Please help

So you got your moms up top on an 18 hr light schedule and flowerings on the bottom.

Youre right to be worried about light coming from the shared duct.

Why not make 2 systems, you have 2 fans.

If your bottom tent has vents(it should its a secret jardin, but I have a DR not a twin so not sure) but it should just hook the carbon filter and one of the fans(the more powerful one if theres a difference between the two) and use that as an exhaust and use the vents as a passive intake. Basically the negative pressure caused inside the bigger tent will cause air to suck in passively without the need for an intake fan.

Now take the other fan and use that as an exhaust for the top tent(does top tent have vents?)

The only reason was to save money on carbon filters I have to stay covert and it is hard to get supplies in my area but another 70 dollar filter is worth the peace of mind I will take your advice. I think that will work good I can use a passive intake on both tents. Thank you and rollitup.org I am literally in the middle of nowhere and this forum is awesome. The self proclaimed experts that I know personally are full of shit half the time and think that their way is the only way. You and others like you are have saved me time and money and saved me some serious mistakes for my first grow.