I'm in California. It's been hot here also. We free range about 8 hours a day or so. We had chickens many years ago and decided to get some again last year. I've got 5 girls about 9 months old and 3 chicks coming soon.
They do need to eat about 90% of their lay feed. Do you think they are getting too much grass or other snacks? Another reason for soft shells is stress which might be why they are laying from their roost?
Squatting is usually a test by putting your hand over them. Once they are ready to lay, they do that to let the rooster hop on. Lol. I'm not sure about marans, but my earliest chicken laid her first egg at 20 weeks.
That's a tough one. If you can check on them occasionally and see what they are doing. If they are snuggling all the time without a lamp, then I would put it back on. I've read that chickens regular temperature it 107 degrees, so 70 my be pretty good to them.
Beautiful girls! I don't think you'll notice much difference in upkeep for one more. I don't know about Australop, but my Barred Rocks are great birds. Very easy going. I originally wanted 3 chickens and wound up with 5. They are about 9 months old. I have 3 new chicks coming soon...
Yesterday was the 3rd day with the mister in the yard. They were all pecking the ground near it. They are getting used to it being there. Just about my whole yard is covered by trees so I don't think they need it, I just thought they might like it.