I've used Citadel, Vallejo and Tamiya paints. All are acrylics, but vary due to differences in pigments and suspensions. Some have more colour pigments, and some are finer pigments which will allow for decent coverage even with thinner coats. ( thinner coats meaning that you thin your paints with water some other medium )I'm primarily a miniatures painter, so trust me on this.By mixing your paints, I'm going to guess that you're meaning combining them on a palette to create custom colours. Most paint brands won't mix well together, but basically you can do it as they are all acrylic based paints. An acrylic paint is an acrylic paint. ( to put it VERY basically )I'd say to experiment a bit and see what works. ( I know from experience, as I've done it... you CAN mix Citadel and Tamiya paints together. But I'd only do it if I had no other options. )Now if you're asking if you can layer two different brands of acrylic paints, then my answer is definately a resounding yes. As I stated above, an acrylic paint is an acrylic paint.Hope this helps, and happy painting.