Old Man Novice

From one "Old Man" to another welcome to the forum. 
It would be a help if we knew the of the make of inverters.
Just a guess from the above info, I suspect you are running SunSynk / Deye  5.5 kW and 3.6 kW inverters, and you're son-in-law has 2x SunSynk / Deye  5.5 kW inverters in parallel. (Master / Slave inverter)
If this is true, you're inverters can usually have 2x strings of 8 panels per string in series, but check the panel voltage VOC does not add up to over 425V.
You're son-in-law can have the same for both inverters, i.e. each inverter can have 2x strings of 8 panels per string in series.....
Enjoy the journey. 😀

Welcome Sir!
Jay

Welcome to the forum you are in good hands.
To answer your question above on both mentioned installations you will use series connected solar panels only as you are most probably running high voltage mppt's. As @TimCammentioned it is a safe bet running 8 panels in series(string) to stay within the maximum input dc voltage of your Scc especially with lower temps.Solar panels in series the voltage(Voc) is added up and the total current will be the Imp on your panel rating decal. What is advantageous of series connected strings you don’t need thicker solar cables 4mm² will suffice saving you some mullah.
Normally a combination of series/parallel configurations will be used on low voltage mppt's like the Victron 100/50 smart Mppt controllers or some of the Voltronic inverters. Once again lower voltage higher current accomplished through series/parallel combinations but thicker solar cables will be needed costing more money. Care need to be taken with series/parallel combinations not to exceed the short curcuit current of the Scc specified by the OEM and to use series fuses on each panel should the array current exceed the specified panel fuse rating. 
Hope this makes some sense should you need spesific calculation values supply us with solar panel manufacturer, and spesifications eg. Post picture of panel rating decal and inverter side label.
 

Welcome to the Forum.

There are lots of people here with technical skills and who are generous with offering advice. I am not one of those people. I am just a guy who has had solar for a few years and so some experience to share.

The obvious thing that seems to elude a lot of people is that you maximise it's potential by doing as much as you can whilst the sun is up. So there are rules in my house - chiefly that we don't run appliances after the sun has gone down. The dishwasher is full? Well it runs tomorrow morning. Once the sun is down you are using stored power from your batteries. During the day you are getting free energy, and if your experience is anything like mine, you don't use most of it. My battery is usually fully charged by about 11:30, then the system draws just enough to service whatever the load is. 

When I had a solar geyser at another house, I learned that the way to maximise that was to change our routines. So (one example) we told our housekeeper not to start the day with washing stuff, but wait until about 11 or so. Evening showers instead of morning.
Use the sun as much as you can. There will be an element of trial and error in this, but you will figure out the sweet spot between servicing your needs and keeping your bill down.

Also read the manuals for your appliances. My dishwasher has several modes, and they all use different amounts of water and electricity. Don't do hot water cycles on your washing machine if cold does the job (for us it does). Things like that.