Assuming the Ranger is 5 metres across the beam (based on a rough visual comparison with the size of the Endurance which we know to be 64 metres in diameter), the G-forces the crew would encounter at 70RPM are around 5G, high but within the tolerances of a trained NASA pilot.
The official novelisation concurs that whilst it wasn't pleasant, it was at least survivable...
He felt the retros fire, and the lander started to spin, picking up speed quickly as both ships streaked toward the waiting ice below. The g-forces increased, as well, pushing them against their restraints, trying to crush them. Cooper felt the blood rushing away from his head, and struggled to remain conscious.
They weren’t falling cleanly anymore. The atmosphere was pushing back, and hard, bouncing and yawing the tiny ship. Mann’s planet seemed to be everywhere, and the curve of its horizon was fast straightening out.
He saw Tars open the airlock. The Endurance was still spinning relative to them, but slowly, as they neared matching the rpm. After several heart-stopping moments they lined up, and Tars fired the grapple—but they hit an air pocket—the hatches went out of line and the grapple caught nothing.
He glanced over, saw Brand had passed out, and knew he wasn’t far behind her. He fastened his eyes on his instruments rather than the wild whirling vista of Mann’s planet that was moving into and out of view. He tried to hold on.