Wow.
How do you lose 20lbs in 5 weeks?
That's 4 pounds a week, or half a pound a day. You have to burn 3600 calories to lose one pound of fat, so that means his caloric deficit is 1800 calories a day!!
He's running about 100 minutes a week, so that's only 15 minutes a day. So this is 200 calories a day? Maybe 300 if he's really heavy?
He must weigh hundreds of pounds and be eating very little food -- an amazing job of losing weight. Congratulations to your friend.
I would say, do whatever is least stressful. 25-35 minutes/run isn't bad for a beginner, and if he's at risk of injury it's probably safer for him to add more days. As far as fitness is concerned, at that level there just isn't too much difference between adding more days of running and adding more time per workout. One thing he *should* do, however, is prepare for the race distance. How far will he be running in the marathon relay? He should get close to that in practice. If it's significantly further than he's ever run, he should pick one day per week, maybe every other week if there's enough time before the race, where he goes a bit further in training to build up to that distance. That would be his weekly long run.