Im actually using those exact servos in an E7, so in my opinion they will work fine in the 696 on regulated voltage. The 696 is very light, and doesn't require super high torque servos. Regarding the tail servo, You would need to step down the voltage. If it were me I would use a servo capable of running on the same voltage as the cyclics. That way you can set your bec to 6v for everything. Also pretty much all tail servos nowadays run at 333 mhz or higher, i ran into an issue with a particular fbl unit that could not be turned down enough to run an older servo that was only capable of 200mhz i think, and it overheated. Plus the torque rating on your jr is low by todays standards and has a plastic output gear. I would save that servo for another project 😁
Hope this helps!