Adding two 240 Circuits
I wouldn't recommend working in a live electrical panel unless you are very experienced and understand the considerable hazards.  Especially in this situation where there is no obvious upstream overcurrent device.  Slip with your screwdriver and you could have a pretty serious fire, arc explosion or electrocution.

I highly recommend consulting with a electrician licensed in your area.  Not just for the task of adding the circuits but also to investigate why there is no upstream overcurrent device/disconnect. (edit: ThreePhaseEel reminded me of the "Rule of 6", where a panel does not need a main breaker if all the power can be turned off in 6 switch flips or less.  This installation may be correct under that exception.)  

If you are worried about cost you may be able to reach an agreement with the electrician where you do the majority of the work, with them just doing the final hookups.  You'll stay safe, and guarantee a safe installation.

As to your question you cannot know if it is correct to connect the ground wire to the same terminal bus as neutral without knowing more about the overall electrical system.  Neutral and ground should be connected (bonded) in only one place, usually the main panel.  If this is the main panel, ie the two heavy gauge wires in the lower middle come straight from the utility or meter, the installation is probably correct and you can wire additional circuits like the range circuit is wired already. If this is a subpanel (perhaps in an apartment or multi-tenant situation) the panel may need to be corrected to separate neutral and ground.