The will bend horizontally. It will behave like a tension ring. The block will crack and, once it does, the rebar will be engaged in tension. It will bend in between the ends and it will have global tension.
You will still need 8" or 10" block (it will depend on the amount of reinforcing put in). I can offer this complete design as an additional service, if you're interested.
You're not thinking of this correctly. You're thinking of a single wall being pushed over. That is not the behavior that will occur. The wall will span horizontally to the two other walls, not vertically as a cantilever.
The wall alone can resist almost no pressure as a simple wall the way you describe it. It would need a properly sized footing to resist the overturning.
Additionally, think of this, or actually try it. Blow up a balloon partially. This is a rough approximation of your condition. Now put half of the balloon into a semicircular wall so that one half of the balloon can't move. Now continue to fill the balloon. To say that the behavior of the balloon changed is not correct. The entire balloon still expands, putting the entire surface of the balloon into uniform tension. Your situation is very similar. The water imparts an equal pressure on every single surface it touches, whether it's restrained by soil from the outside or not.