There are several EV chargers that can integrate solar PV charging, i don’t know them all, but do know the Zappi, and the Andersen A2, both can manage PV charging, which is probably the “integrated” you were referring to.
I don’t have any electric showers, got rid of them years ago, however, my understanding with the Andersen, is that the normal charge output of 7kw, is reduced, if a high demand item/s are turned on in the house. The Andersen has load management built in, many others also have this facility, so it would reduce the charge to the car, until the internal household demand, reduces, or stops. This is all automatically done.
In practice, this is a short temporary reduction in charge to the car, so, i have noticed for example if we had a washing machine on at the same time, and say an electric kettle, the charge to the car will reduce, until those items reduce their demand, or are turned off. In practice, we are talking minutes.
Its not in any way an issue for me, as any reduction, is temporary. In any event, most newish EV’s have at least 40 kw batteries, so its going to take 6 hours minimum to charge from empty, so a washing machine on at full spin, only lasts say 15 minutes, and one can schedule charging via the app, to take place at night, or at a time when those household loads are not happening.
I can only charge one of the cars at a time from the charger, i charge once every 6 to 9 days, so its not an issue at all for me. I do have an external weatherproof 3 pin socket- out front, so could in theory, charge the other EV at the same time. As its 3 pin, its a much slower charging rate of around 3kw,so would take more than twice as long to charge the EV, but have never had to do this.