One way would be to keep the hills to the hill sessions & the long runs to the flat bits. That way you get quality hill sessions, focussing on strengthening the muscles you need, then elsewhere in the week a quality endurance run, prompting your body to make the necessary adaptations.
By combining them you may end up working at too high an intensity on your long runs, and still being weak going up the hills.
I'd recommend building up a session to 60 mins on a hilly loop - ~1km up hill, 1km down hill. Start with something like 2 x 20 mins with a 5 min jog (on the flat) inbetween & over time upgrade your session to 3 x 15mins, 3 x 20m, 2 x 30m, 1 x 60m. If you're not used to running hills, I'd recommend giving your calves / achillies a good stretch afterwards.