I would say start of with little a few times a week. I wouldn't suggest going all in at one time because it can be very stressful and tear your body down more than anything so take it slow
Start with telling him you gotta start getting it together life’s not long and put him on a playlist , and start walking for 7 days for 25 minutes then build up from day 1 then after that week start with sit ups and walking again if okay with jogging that do that , my personal fat burn is fast exercising where you have a rope a power clean bar and weights and you use the rope to swing it and down as fast as you can till you can’t , and power cleaning with light weights than build up
