A high powered blender will crush the seeds, but if you prefer a completely smooth fruit layer with no bits of seeds then strain the blackberry puree through a fine mesh strainer.
We experimented with a couple layering techniques. I preferred #1 with smaller amounts of each layered more frequently, while Eric preferred #3.
1. Cream Cheese, Blackberry, Cream Cheese, Blackberry
2. Blackberry, Cream Cheese, Blackberry
3. Combine the two mixtures and swirl together.