Find replacement handles for windows from 1956

You would not need to have a jack to be able to lift something up. Through the use of some pieces of framing material (such as common 2x4's as they are called here in the USA) you can pry and lift things with relative ease by the mechanical advantage of a lever. Cut the vertical piece to just the right length for the application and then with the help of at least one of those four friends you may be able to get the upper window into place.

Some things to think about with this.

1) The window may actually be stuck in its frame and unable to move. The wood over the years could have swelled and locked the window in place.

2) Coats of paint applied to the window and the frame may have locked in the window as well and thus not be movable at all -- unless the paint was all removed first.

3) If you do try the lever bar approach shown in my picture make sure to apply the pressure to the window near the frame under the side rail of the window. To apply in the middle away from the rails will put undue pressure on the glass and could result in breakage and / or personal injury.

4) Applying excessive pressure in one spot, either on the window itself or on the sill area below can damage the wood. This would be especially true for windows that are made of softer type woods like pine.

5) When using a lever scheme take the time to plan out the activity and how it will be setup. Without careful setup and applying pressure to the lever in the correct direction you could cause the fulcrum board to kick out sideways and pose a danger to either yourself, the window glass, something outside or someone below the window area.

This type of locking mechanism is a sash latch. From the picture it looks like it's not installed in the way sash latches are typically installed.

Usually this type of latch is attached to one of the sashes of the window. Here is such a latch on one of my sash windows:

You can see it's not installed into the frame like yours, instead it's on the end of one of the sashes and latches into a bit installed on the other sash. In some windows, like my basement windows (not pictured) both sashes slide, in this window I took pictures of, only one side slides. Here's a better look at the lock's position within the entire window:

As you already know, your particular latch is older and while you will probably have difficulty finding this exact model from a retailer you will likely find modern equivalents that may fit. As @keshlam, and @Comintern noted in the comments technically this latch is not appropriate for your window. Buying a new latch and installing it into the frame in the same way as your old latches could result in them breaking the same way. If you go with this approach I would recommend that you search online or bring the latch with you to a store to find a new latch that matches in dimensions and see if you can find something made out of a durable material.

Another approach that @Ecnerwal mentioned: there's no rule that says you need to use the same style of latch. If you're not keen on replacing the entire window(s), you can buy latches that are appropriate for your style of window. From your picture it's not clear if your windows are sash windows (they slide open) or casement windows (they open outwards on a hinge). My guess is they are casement windows in which case there are many options available to you. Again, you can search online or bring your window measurements to a store to find latches that will fit and suit your style.