Sealed boxes produce a tighter more accurate bass, but the bass is flatter and punchier. A ported box will generally produce a deeper and more boomier bass, but they can retain a decdent amount of accuracy as well, but not as accurate as a sealed box. In short a ported box is louder and a sealed box is more accurate. The Brahma needs a small box since ur giving it 1000 watts. maybe about .9 cu ft^3. At Adire AAudios website there is a table that tells u wat size box to use according to how much power ur giving it. the table only covers sealed boxes tho.
Personally, I prefer the ported Boxes. But currently I am using a sealed box. its all preference. remember to also take size into consideration. Usually a ported box will be bigger than a sealed box. I kno tho that the Brahma only needs 400 watts for maximum excursion as long as ur sealed box is pretty big. In that case a ported box could end up being smaller but then again u would need more power.
No i would not recommend that because if they are close to each other they could throw off the sound. Im not the smartest when it comes to boxes but i would not recommend that. if they r going in a trunk then i would say to try and stick w/ one kind or the other. I guess u could kind of say that a ported would be best but those Brahmas would slam in either type of enclosure. try and decide on 1 kind tho