Changing Music on a Cuckoo Clock Movement
There are lots of very cheap sound circuit boards you can order. Many of them can store multiple song movements to be accessed separately. They are very cheap and relatively easy to "program" with audio of your choosing. But they would have to be adapted to these clocks.

These clocks almost certainly include something quite similar, but custom pre-programmed. You might get lucky enough that boards you can find (from China, Taiwan, etc) are very close in terms of voltages, connections, etc., that they could be easily applied to the standard clock to re-make it in your desired image.

But you might be unlucky enough where the circuits/boards they use are different enough that it will take at least some very specific design knowledge in order to adapt them. In fact, that's a likely scenario. And for that, you will first need to get someone who will examine a standard clock for you and tell you how likely that option might be. And then, if you decide to go there, would be responsible for completing the project for you.

In short, my recommendation is that you break things into the following steps:


Find a consultant, one that you can count on to complete, to examine one of these standard clocks with the standard song choices. Ask them to prepare a report or plan about the next steps available to you. This report will include the results of their examination (what kind of method is used in the clock to trigger the songs and/or select them) and perhaps one, two, or even three approaches that might succeed in achieving your goals. Those approaches should include some idea of the downside risks in terms of time and money, as well as the upside benefits. Make sure the consultant realizes that you may, or may not, select them for the final work and that you want a report that can be taken to others for the purposes of bidding the job, if your group decides to go that way.
[See text below (*)]
Sit down with your group, study the report, and decide on a course of further action. Then follow through, either with your consultant finishing the project or else bidding it out using the report as a basis.


(*) If you want to see if EESE can be used as a cheap source of advice, that report would go a long, long way in helping others here understand the situation better. And you can then get a lot of free kibbitzing, which may or may not help much. So you could insert a "kibbitz" period before bidding out the project or hiring your consultant, I suppose. But I wouldn't count any chickens here and it may only wind up delaying things or adding emotions to an already emotional situation, perhaps. Up to you.