Window does not stay up
Hello,
We can't be sure of the tilt latch you need with the original still installed, but the 26-243A and 26-244A would be a good place to start. The top is squared, but the bottom has the same curved shape needed for installation. Note that these latches have a straight locking tooth, while yours looks like it might be curved. If so, this could cause interference with the balances in the side jambs.
If your windows won't stay raised, that indicates that you may need new balances as well. If so, we would need to see an intact version uninstalled, including both ends and the stamp code, to compare to our inventory. Thank you!