If you think pork butt suffers when frozen and reheated, take a look at this pic. I like to cut a barbecued pork butt into quarters and vacuum seal and freeze each portion, then later thaw, gently reheat, and pull/chop a portion.
We have the same situation just the two of us. Although I usually only buy one individual butt at a time if there on sale and if we do get two I just freeze the extra one whole.
If I do ever get a Costco twin pack I will certainly use your method.