Nest setup | 6 wires but no C-Wire

My parents Honeywell broke, figured I’d upgrade them to a nest. Was going to use the C Wire adapter, but I believe thats for a 4 to 5 wire setup. They have 6 here. Any advice on how I can set this up? The controller by the boiler is also a Honeywell. Am I just better off getting them a replacement here?