Assuming you have summer tyres, there will be 3 readings on the tyre pressures chart : lightly loaded, lots of luggage and an eco setting
The chart is based on adults of about 70kg and something like 15kg per suitcase. So Fully loaded with 5 adults and luggage adding about 300-400kg. However 5 children will be about half of this so I would suggest going midway between the normal and loaded setting.
There really isn’t any advantage to going higher, what (very) marginal fuel saving will be more than offset in costs of maintaining the tyres because you won’t wear the tread 100% evenly if over inflated.
Remember for a big heavy vehicle like this you need to be swapping the tyres front-back at intervals (the handbook suggests something like every 9000 miles), but in practice anything upto about every 14000 that fits in with when you have chance to do it (or when it is being serviced).
Of course if you are driving other peoples children around for a living, using summer tyres in winter is very bad idea, so just get the tyres moved when you do seasonal changes. (Modern eco summer tyres are not designed to work in cold rain, frost, sleet, snow etc). You will either need a set of winter wheels & tyres, or dump the tyres the car came with and buy set of all season tyres, or do nothing and expect to skid or crash in winter weather.