Pretty sure the nyassae would interbreed. If I were in your shoes, I'd sell the jakes and focus on the Leth. Albus. They are stunning and when they breed, I'm sure you'll find it VERY EASY to sell fry/juvies. Eureka Jakes are a dime a dozen in our area. Market is currently flooded with them. Leth. Albus, not at all.
Best of luck! I'm still mourning the loss of my Leth. Albus Kande male! Stunning 4". Will get my hands on more the minute I have more tank space!