My family of 6 leaves Gatwick at 9:15am. We are staying in London up to our departure date. I'm trying to figure out if I should get a hotel closer to the airport the night before or is it possible to get a train early enought from London to the airport. Or I even thought of visiting Paris and getting flight from Paris to Gatwick with a short layover until our flight leaves at 9:15 to maybe bypass a hotel the last night, since we have to leave so early. Any suggestions would be greatly appreciated.

For a family of 6, it probably makes sense to use a car service like justairports.com or Ray's london-transfers.com. You can then schedule a pickup at your hotel as early as required to get you to the airport for your checkin.

ditto to above but trains run 24 hours to Gatwick I believe from London Victoria and very earlier in the morning from other stations like London Bridge, Kings Cross, etc.

"getting flight from Paris to Gatwick with a short layover until our flight leaves at 9:15 "

There aren't any flights between Paris and Gatwick so that's a non-starter.

Unless your flight is Sunday I wouldn't recommend a car service from central London as it will be VERY slow.

Depending on your start point in London take either the Southern Trains service from Victoria or the FCC train from St Pancras or London Bridge. You don't need to use the Gatwick Express and there are normally trains very early in the morning which will get you to Gatwick for 6:30am

Thank you for your help. Just knowing that trains run 24 hours and we have a way to the airport, we will most likely stay at our hotel until Monday morning and take an early train to Gatwick.

You could stay at an airport hotel - the Hilton is situated a the South Terminal, and the Sofitel at the North Terminal. Otherwise, take the Gatwick Express from Victoria station direct the airport.

You can check train times on www.nationalrail.co.uk.
There are trains to Gatwick Airport from London Victoria throughout the night, every half hour from 0300, then at least every 15 minutes from 0500.