We are going to come to Gatwick Airport 04.29.2018 at 9.35 pm in the evening to the North Terminal and have next flight in the morning, by EasyJet, 04.30.2018 at 9.05 a.m. to Marocco with all hotel bookings in the hand from the South Terminal. We are planning to have a night in the airport transit zone. Do we need any visas in this case to get from one terminal to another? If some of us have British visas could they take the baggage for the entire group and re-check it? Easy Jet have online ticket. Will it be ok without going outside transit zone?
It does not appear to be possible to transfer airside between terminals at Gatwick. Note that https://www.gatwickairport.com/at-the-airport/flying-in/flight-connections/ says:
If you need to change terminals, you can take our free shuttle 24 hours a day.
The shuttle they refer to is the landside peoplemover between the North and South terminals.
So in order to reach your departure terminal, you need to enter the UK. Depending on your nationality, where you're traveling from, and which other visas you hold, you may qualify for the UK's landside "Transit Without Visa" scheme, but you have not given enough information in your question to determine that. See this question (and links therein) for details.