It's tricky & expensive to have 2 EVSEs running at the same time, and this also tends to make huge demands on domestic power supply. You need to know what's the max current you can take in your 230V EVSE. In UK EVSEs like this are usuall limited to 32A, as the house often has a 60A fuse and that may need upgrading to 80A or 100A. Once you know what current you can take, next you need to plan how to overlap charging. 1 kWh gets you let's say 5km range, so work out how many kms you each do each day, whether you need to charge both cars every day? If Dad is retired, maybe he isn't driving huge distance and can fit-in with whatever commuting you may be doing? If you can fit in a changeover at decent time of day, that's easiest.
If you can't manage this, maybe you do need 2 EVSEs running at the same time. Suppose you have 32A supply (7kW) for your EVSEs. So you could have one simple, dumb one running at 16A, and a 2nd 7kW-variable one which has a current-sensor that monitors how much current the house is taking, and limits the current so you don't blow the house fuse. So that could run at 32A max, but be restricting it if demand is high. So you charge Ioniq 28 at 16A (3kW) for 8 hours starting at say 6 p.m., so at about 2 a.m. that will finish charging (24 kWh appx), and the 32A EVSE that was filling Tesla at modest 3kW for the same time, can now increase to 7kW for the rest of the night, so Tesla gets 24 kWh during 1st part of night, then after 2 a.m. to say 8 a.m. it gets 7kW for 6 hours, = a further 42 kWh.
Allow 10% loss in the charging process, e.g. my Ampera takes 12 kWh to fill & give it 10.4 kWh useable.
Others here can probably suggest EVSEs that do power-monitoring.
If you have 3-phase supply, you could run 2 32A EVSEs off 2 different phases, but that's a very beefy supply!