I don't know why it will not work. is it because maximum sink current is 16mA or s it because outputs are open collector?
Referring to ohms law, you would need a sink current of > 70 mA in your circuit, considering 5V supply and no additional load impedance. You have been talking however of 9V supply.
Open collector is simply unsuitable. You should go for a low impedance impedance push-pull driver. Your previously suggested discrete transistor circuit is basically of this kind, although I'm not sure if cross-conduction may occur in the particular circuit. My personal favourite would be a high current gate driver like TC427 or TC428. For a single ultrasonic transducer, standard CD400x CMOS devices are usually suggested, but you'll need lower impedance/higher output current for the parallel circuit.
There's nothing against using a number of CD 400x ICs, of course, e.g. CD4049 inverters.
what is the maximum voltage I can use to drive them?
The linked "data sheet" mentioned 20 Vrms. Murata in contrast only specifies 20 Vpp square wave for it's newer 10mm MA40S4R/S, corresponding to about 10 Vrms. You should however consider the voltage "amplification" achieved by the resonant circuit. So a 20V supplied H-bridge with series inductor may be already too much.
But it's not clear, how the maximum ratings have been exactly evaluated. As I already mentioned, there's an absolute level set by the piezo depolarization voltage. You would need to know the piezo disc thickness for a reasonable estimation. Below this limit, either breaking or wear in long term operation may occur.