The reason for your confusion about the low end extension of small-woofer systems is that the frequency response specs rarely indicate how much acoustic output they can support at those lower frequencies. For example, a 6.5" driver and a 10-12" driver may each play a 30Hz tone but the latter can play it much louder. Note that the drivers in the subs you list are larger than 6.5".
Also, you should consider using a much higher crossover than 35Hz for several reasons.
1. Crossover roll-offs are gradual. A 35Hz crossover will have minimal attenuation one octave down and, with your speakers, have little effect.
2. Raising the crossover will transfer more of the LF power demands to the more able sub, reducing stress and IMD in your main speakers.
3. Raising the crossover and getting a sub with decent EQ will make placement easier and integration smoother.
However, how do you intend to connect and crossover the subs?
Also, you should consider using a much higher crossover than 35Hz for several reasons.
1. Crossover roll-offs are gradual. A 35Hz crossover will have minimal attenuation one octave down and, with your speakers, have little effect.
2. Raising the crossover will transfer more of the LF power demands to the more able sub, reducing stress and IMD in your main speakers.
3. Raising the crossover and getting a sub with decent EQ will make placement easier and integration smoother.
However, how do you intend to connect and crossover the subs?