I would like to control four or five Arduino with single one com or something. They are about ten feet apart each other.
You can control them from any computer with serial port (yes, including Raspberry Pi) if you use some single master multi slaves protocol. On electrical level it can be RS485 - either 4 wires full duplex or 2 wires half duplex. So you will need 1 RS232-RS485 convertor for your computer, and one for each Arduino. Make sure that your Arduinos have RS232 and not only USB, otherwise you will need different level convertor like TTL-RS485 or USB-RS485). On protocol level it can be MODBUS RTU or ASCII, some other protocol, or even your own if you want to keep it simple. To be able to talk to everyone, all sides need to have unified electrical connection level and talk the same protocol. There are MODBUS libraries available for FPC and as Arduino C libraries. E-Lab AvrCo Pascal compiler has it, and I think that I have seen one for mikroPascal. Your board will have different MODBUS adresses, and when your PC asks for data from board 1 with address 1, only board 1 will answer. Then you ask for data from other boards one by one.
I thought I could use IC2 but it is my understand it will not work if it is long distance.
I2C can have extended range with little electronics, but how would you interface it to PC? You would need something like BusPirate or custom hardware, so I would not recommend it. Keep I2C just for connecting Arduinos to their local sensors.
I was thinking to use ENC28J60 with Nano. Can we use five ENC28J60 with Nano and switch hub to computer with FPC. If we can then how do we do it?
Unlike W5100 and similar, ENC28J60 is a very simple chip capable to talk just UDP. However some libraries extend it and add TCP/IP layer and other popular protocols. You can talk with ENC28J60 from E-Lab AvrCo pascal, mikroPascal and Arduino C. All boards and your master PC should be connected to a ethernet switch. Your PC would then just need to call boards one by one in a loop and request data from them. You can use MODBUS TCP protocol for ethernet, but you have very limited resources so you might want to keep it simple and light and instead implement your own request/reply data exchange protocol.