How to GFCI-protect a 3 gang box where each receptacle is on a different circuit
First, "GFCIs", it sounds like you are talking about the "GFCI + receptacle combo device" readily available all over.  While that is one way to provide GFCI protection, it can also be provided by a GFCI device upstream.  Any GFCI device can protect all downstream loads.  As such, GFCIs come as 


a GFCI+circuit breaker combo device
a GFCI-only device (deadfront, looks like a receptacle but with no holes)
a GFCI+receptacle combo device, if having a receptacle on that circuit is allowed there, which in the case of kitchen receptacle circuits, it is not. 


So for instance, providing GFCI protection to a switch obviously can't be done by a GFCI+receptacle combo device at the switch location.  You need to find an upstream location and install a GFCI device.  

You said "GFCI protect your 3-gang box", and it doesn't work that way. Boxes don't get GFCI protection, outlets do. (an "outlet" includes any electrical tap, including hardwired loads such as a light or disposal).  This box has a mix of things that do, or do not, need GFCI protection. Lighting generally doesn't need GFCI protection.  A disposal may, but putting it downstream of a switch is bad form, as some GFCI devices don't like their power being interrupted.  The better location for that GFCI device is upstream of the switch. 

Home inspectors are particularly awful about spreading this "GFCIs are receptacles" myth. . If they don't see a "Test" and "Reset" button, they tell you it needs a GFCI there.  This is why "GFCI protected" stickers are required on plain receptacles whose GFCI protection is sourced from upstream.  Unfortunately, some people consider them unstylish, and tear them off.  Get more.  You can also make them with a labelmaker, they need not be blue.