1) I think Richard had already explained in in the other other thread. You see two curves because the y-axis limits do not match. At the left you have 5.0 (ksi) as upper limit, but on the right you have 40 (MPa). Set the right upper limit to 100 and watch what happens. Then set it to 34.4738 for a surprise (Explanation: 5 ksi=34.4738MPa)
If you don't want to change the limits you can also delete the limits on both y-axis and let MC chose them automatically. If you now turn off autoscaling for both y-axis you also get what you want.
BTW, As there is only one curve per y-axis plotted and both share the same x-values, you do not need to write the x-values twice.
2) You should read Richards explanation about plots with two y-axis and how the x and y values are assigned. In your second plot you plot 12 curves (6 with the left and 6 with the right y-axis) but you have only 6 variables at the x-axis. Its the same error you made in the sheet in the other thread.