not a good idea to say the least. Never mix subs... If they were being powered by the same amp, then one sub would see more power than the other. It doesn't matter if they are in different boxes. never mix subs
long story short, the amp would put out its rated power for that particular ohm load and the amp would not be harmed so long as it was stable at the final ohm impendance. One sub would be louder as the power supplied by the amp would have less resistancetraveling through the lower ohm voice coils..
When mixing subs with different t/s parameters you run into cancelation (as well as other) issues which is not going to help the overall preformance of your equipment.