I did combined mission to Eve and Gilly once, just simpler then your plan - to get prove+rover to Eve without return and to plant a flag to Gilly and return. I used aerocapture on Eve to get to highly elliptical orbit with Ap beyond Gilly. At Ap I decoupled probe/rover and rised Pe of the main ship above atmosphere. The probe/rover then flied to Eve atmo and land on parachutes. Then I intercept Gilly with main ship, got to low orbit and land with a small lander. After return I wanted to go back to Kerbin. Because I didn't know how much those maneuvers will cost, so I played it on the safe side with my fuel. The rocket has cca delta-v of 7700/12000 m/s (atmo/vak) at the launch. So after return from Gilly I had enough fuel to go to Moho and Dune/Ike and do a flyby before retuning to Kerbin.
