If you have a mango tree you should have pretty warm weather compared to a whole lot of us. At last that’s working for you.
What does a hen do in the wild? Don’t know, but I can base some guesses off of what I’ve seen. Most of my hens take their chicks to a corner of the coop and sleep on the ground in a protected corner. So many do that I’d assume that’s common in the wild, find a protected spot on the ground and sleep there.
On rare occasions I have a hen try to get her chicks to hop up into a nest maybe a foot off the floor of the coop, usually not the nest they were hatched in but another. If the chicks make it, and they often do, they sleep there for a while and make a royal mess of it. If they don’t all make it, and sometimes some chicks don’t, the hen might ignore the ones that don’t make it or she might bring the others back off the nest and take them all to a corner of the coop. So yes, some have different instincts there, survival of the fittest or mothering them all which might mean moving to a less safe position.
The earliest I’ve had a broody take her chicks to the roost is about two weeks. They had no real problems getting up there at two weeks. That was in summer. Some were under her but some were totally exposed. Nighttime temperatures were in the 70’s. They all did fine.
I’d expect that broody to start mothering her chicks the next morning, but yeah, what do you do. I’m assuming they made it without heat so that’s not an issue. But I’d think protection from the elements, rain and wind specifically, and predators. The chicks are really vulnerable out like that.
One option is to lock the broody and chicks up together in that coop overnight. I don’t know if you have a pen around it where you could leave them in there permanently or if that involves catching them every night. I’d think after a few night s of doing that the hen would catch on, but who really knows. They are all unique. It depends a bit on how steep that ramp is but the chicks should not physically have any trouble getting up there if it’s not too steep. The problem may be that they can’t figure out how to get up there. Some are just better at that than others, even with other chicks showing them how.
Another option is to put a shelter under that mango tree. Lock the chicks in here at night, with or without the broody. I’d expect the chicks to learn to go in there on their own at night pretty quickly. In a surprisingly short time I’d expect the chicks to start following the broody up to the tree.
Another option is to just raise them yourself in a brooder.
I have had a broody totally wean her chicks as early as 2-1/2 weeks in the heat of summer. You might be looking at something like that.
Good luck with it. That’s a challenge.