Need help badly........ ...........tell what i need to stop the air suction.........

Okay....i have 2 8inch fans blowing thru my lights........with a 12 inch fan pulling ..........i have to 12x8 inch holes in my walls with 6 inch adapters with 6 inch ducting to allow free air movement......which i though would allow the 2 fans to pull air from them since they are free air vents.....but what happens when i turn the fans on ......the room starts to pull in ......i have 3 soild walls with white mylar on them.....then i have 1 wall made of the white mylar....the room just sucks in.....i put a piece of tissue to the vents and no air movement at all.............i was thinking of attaching 8 inch ducting to the fans and attach it straight to the 6inch ducting of the vents and pull it straight thru....but what about the having fresh air in the room.....?.......need answers quick because this is the flower room....and i just placed them there without checking the ventilation with the mylar wall.......

I'm really confused as to what you mean by the room "sucks in"
Where are your passive intakes coming from? Are those holes from another room in your home or are they going into an exterior wall of your home? If your vents are going into a wall with no inlet from the other side you're most likely not getting air flow because of the posts in your wall blocking the air flow. That'd be my guess, but, I'm still not 100% sure as to what you mean here....

(pic 3) the vents intake from the outside air.........i'm getting alot of air pockets between the mylar and wall.......and i'm not feeling any air being sucked inside from the outside when .....when i step outside the room and go outside to where the vents grills are located.....put a piece of tissue there to see if it has any movement and it doesnt......Im also going to try and tape the mylar to the ground where it lays or should i trim the excess off.......where the bottom wall meets the floor........? one more thing....the room is not airtight..........

Could you post pictures of where your intakes are? And where are your passive intakes run to? Are they bringing air from another room in your house or what?

sounds like you need bigger intake holes