I am sure you have noticed that Flysky do not have any receivers capable of more than 12 channels. Well there are ways. The simplest is to use one or more CEV4's, I will deal with them elsewhwere. Next, there are two options to link two receivers and use the second receiver on the higher channels.
I have dealt with binding an FGR12 and an FGR8 elsewhere as a straighg bind so I wont repeat that. There is however another way of using some receivers (FGR12b, FGR8B, FTR10 and FTR16) as a PWM converter. A PWM converter takes an IBUS single and converts it to PWM channels starting at a channel specified by you. This means that you can overlap the receivers and have outputs for say channel 10 on both.
Once you have made a receiver a PWM converter it will no longer act as a receiver, you can get it back so I will first show you how to do that. All the receivers have a forced update mode. On receivers with a button you press and hold the button whilst applying power and for at least 10 seconds ( until the flash changes). On an FTR 10 you use the bind plug in a horizontal position between bind and servo signal pins.
once there go to the RX set up menu.
select receiver update its a ways down the menu.
then select your receiver type
and click update make sure all is ok and and click OK in the box. The receiver will be updated and the led will flash a different sequence.
So now we have a healthy receiver so remove power and move the bind plug the the bond column so we can bind the receiver.
Now go to the RX bind menu and bind the receiver in classic mode.
The receiver light should change to a solid light.
To turn the receiver into a PWM converter we now need it back in bind mode so remove and reapply the power then go to the config RX as PWM converter menu.
Here you can set the start channel of the PWM converter using the + and - buttons, then click the config button, the flash pattern will change, exit the menu back to the RX set up menu.
now unplug this receiver and set it aside. Put your second receiver in bind mode and power it up. Bind this receiver in classic mode.
Now you need a double ended servo linnk cable link the servo output to the cable and then to the sens socket on the pwm receiver.
remove the bind plug and power up and test, configure your channels and you are done.