Re: can a GFCI outlet share a box with a duplex?
Yes, a GFCI will fit into a 2 gang box with a standard receptacle.
Not sure what your wiring issue is, your supply line comes into the line side of the GFCI, all downstream outlets attach to the load side. If you have more "load" pigtails than the GFCI has connection points, then you bundle them all together with a wire nut and pigtail it into the load side of the GFCI.
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