Double front doors are generally less secure than a single door due to the doors locking into each other rather than into a frame.
If you have this type of barrel bolt then any force delivered to the doors is going to be delivered to the small screws in the keeper.
How to strengthen your double doors? Well adding deadbolts will only help if the door its locking into is secured so changing the Barrel bolt to a flush bolt preferably with fixings in the side and top will allow you to bolt directly into the main frame.
For maximum security on doors you cannot beat a Rated Security Door, which will also provide a barrier between you and the person outside when answering the door.
Feel free to contact us for free advice on securing your home. 9561 2956