Adding more to 125A Main Service
The breakers will physically fit into the panel, but you'd probably start tripping things whenever the water heater turned on. 

At 24 kW @ 240 V, it's pulling 100 A* on its own. Add in lights, receptacles, fridge, or especially the stove (pulling maybe 30 A*), and you're well over the limit of the 125 A main breaker. 

If you want to install that water heater, you'll need to upgrade the main service - which could mean upgrading the service entrance wires from the utility, the meter, the panel, the wires from the meter to the panel, or any combination of the above. 

Installing the AC unit should be doable, though, since it's such a small unit. 



*the water heater won't actually pull 100 A (nor the stove 30 A) all the time. Depending on your incoming water temperature, hot water set temperature, etc it may not need that much power. The stove only pulls 30 A when all burners and the oven are on. That said, you don't want to have things work ok in the summer but not the winter. Or only if you're using 2 of the burners rather than all 4.