I would have no problem with that myself but for an older couple I would probably not chance that. The BCN flight will depart from 2F while the IAH flight will arrive at 2E which can be quite a trek, and they have to go through passport control (and possibly security, if they're unlucky) on the way there.
That said, there are many daily flights between CDG and BCN so misconnecting and being rebooked shouldn't be too onerous.