Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
The Raymarine ST60 is a depth display. It would be hooked up to a sonar transceiver, from which it would get its depth data.
The Raymarine E7D is a chartplotter and fishfinder, and needs a hookup to a sonar transceiver, too. It might be difficult to get the ST60 and the E7D to work on the same transceiver, and I would presume that you would do better with the E7D only, since it is the more complete instrument.
The Raymarine RL70C is a radar display, and would need a hookup to a Raydome or a radar transceiver or radar array.
The last one is a more difficult case to decide upon... the Raymarine AIS650 is designed with a Seatalk connection (the white-ringed connector, I think), a GPS antenna connector, and a VHF antenna connector. To get it to fully function, it needs a multifunction display to be connected on the Seatalk connection - so it needs a multifunction display with a Seatalk connection hooked up to it, and it also needs a GPS antenna connected to it, and a VHF antenna connected to it. Appropriate connectors for those are obviously labeled on the AIS650, and the E7D multifunction display has a Seatalk connector for connection to the AIS650.
I picture the ST60 being discarded, being a cut-rate past-generation piece of essentially outmoded equipment. I think the E7D has a depth indicator function on it, albeit not so simple and obvious.