Can any of the RF Synthesizers operate as low as 10 MHz?
No, none of the RF Synthesizers operate as low as 10 MHz. The Si4133 IF output can reach as low as 526 MHz without division, i.e. yielding a sinusoidal output. Allowing for division, and a more square wave output, the IF can reach as low as 62.5 MHz.
The I2C programmable oscillators such as the Si570 can be programmed as low as 10 MHz yielding clocks in various standard digital formats. Additional filtering would be required to convert the digital format in to a sine wave if necessary.
Is the Si4133 IF output a sine wave even when divided?
No, the Si4133 IF output is a square wave when divided. This is also true for the Si4126/36 RF Synthesizers and all deriviative devices.