The setup: a chest, one funnel going in and two coming out (only tested with funnels on the side). If items come one by one on a conveyor belt to the intake funnel, both funnels looking out of the chest will deposit an item to the conveyor belt running below them. So one item in, two out. It works if you put one item in the chest manually. If 2 or more items are put in the chest, the funnel behaviour is normal and 2 items get subtracted from the chest.

I tried it, but that not work, i think you can show some screen bc me and my mate have test it