You can make the same line appear multiple times but I don’t think chan_sccp has a way to do rollover from one button to the next as additional calls come in.
If you need it to work that way, you could set the max calls per line to 1 and give each endpoint multiple lines, then configure a “destination if busy” in FreePBX for the first line to point to the second one.
BTW the 7965 is a great phone 