They can try but I don’t think the jury is going to fall for this a pregnant mother killing her two well cared for daughters.
The tv interview is going to help convict him.
It is all rampant speculation based on standard defense attorney motions. IMO it's nonsense. he is not going to retract his confession. I think it will go like Mark Hacking's case - a not guilty plea followed by a plea to first degree murder, later on. Or, he will mount a costly and futile insanity defense.
That's my prediction.