It's very possible for you to drop the ~12 kg's that you need to in order to reach your ideal weight. However, fat loss is best and most effectively accomplished when an increase in exercise is combined with a decrease in calories. While you exercise once or maybe twice a day, you will be eating more often, so it's important to be conscious of what you are eating. Since there isn't any info about what you eat, I'll leave the diet part alone for now, and address your other questions.
The exercise and calorie burn you get from running outside is the same as running inside the gym on a treadmill. However, because most cardio machines keep track of calories burned, it could make the case that it would be a more efficient way of losing the amount of calories you need to in order to reach your goal weight. So unless you have a way of counting calories burned while out on a run, the gym machines would make it easier to know when you've reached a goal amount of total calories burned for that session. Not sure how many calories is enough to lose for one session? Lets go over an example to give you an idea of what you do could do to try and accomplish your weight loss goal.
There are around 7,500 calories in one kilogram, and to get to your goal weight you want to lose 12 kilograms. If through exercise and diet, you can eliminate 200 - 500 calories a day, it will take in between 1 - 1.5 months to burn 2 kilograms. If you can maintain that calorie burn for 6 - 9 months, you will reach your goal in under a year which is awesome!
As for exercises to help you lose weight, the exercises that work the most body parts will burn the most calories. If you have access to a gym, lifting weights would certainly aid helping you lose weight, but if your not into weights, there are lots of body weight exercises you can do to keep yourself in shape and looking good. Examples include: mountain climbers, push ups, burpees, planks, lunges, leg raises, and tons more you can check out here:
While you exercise, you want to keep your heart rate elevated to maximize calorie burn, so aim for at least 15 repetitions each time you complete an exercise. To take it to another level, create whats called a giant set, and complete several exercises back to back to back. Walking is a good way to lose fat, but its not a very intense exercise, so the calorie loss won't be as big, as when you are completing other, more exhausting exercises.
Fat loss can be a very rewarding goal to fulfill, and you'll get as much out of it, as you put into it. However, it's not exactly an easy goal to fulfill, so if it takes a while before you find a routine that works for you and your hectic life, don't stress, just know that with hard work and dedication, you can look anyway you want to look.