Get real evidence of what killed the calves. That's the first step. Before then everything is speculation and has zero value in helping fix the problem. Been around ranchers all my life, what they think killed a calf isn't always what did it. Disease and birthing issues are by far and away the greatest killer and unless found before the scavengers get to it, which can be very quickly, can be difficult to determine.

I take lion sightings with a grain of salt. Way too many sightings around here for how few there likely is.