Fat people make bigger targets...
That said, I spent most of my formative years (up until 14) overweight, but carried that weight and kept up with the skinny kids. When I started work building seawalls and piers, I was working with a 110 lb sheeting hammer, picking it up and driving down 2X10 tongue and groove creosoted boards for the actual wall part of the seawall. Actual weight was more, as the air hose was hanging from that and I was standing on a 6" wide surface as I worked. At the end of that summer, I had lost 10" off my waist, and gained 20# (which really made a mess of my BMI, but finding fat on me was tough to do), and I had problems finding jeans I could get my legs in, and wearing shirts that would not tear down the back when I reached for things or lifted something heavy.
If these people have been active, they can be whipped into shape in a few months, and will be able to carry the gear they will need to.
