As mentioned above, the xray issue is only for unexposed film, developed film will be fine. Also as mentioned above, older nitrate based films were highly flammable, but they would have to be really old to fall into that category. If these are 8mm films (typical for home filming), that would not be an issue, 8mm file was all acetate based.

I would still be concerned about rules being made up on the fly by TSA, so don't attempt to take them unless you have a backup plan, such as someone waiting outside security who can take the the films if they are not allowed through. I would go with gregwiggins suggestion and ship them UPS or Fedex.