Just wanted to say that San Sebastian / Santander / Bilbao to Granada via Madrid is comfortably do-able in 1 hop with a single driver; even more so if two people can share the driving. Use the M50 to route around Madrid rather than the M30 / M40 which route through central Madrid and can be a nightmare.
We had to do the trip in one hop by necessity. We left San Sebastian at 1130 and arrived in Granada shortly after 2130. We had two dogs on board and made use of the picnic areas en route to give them a break and stretch their legs every couple of hours. We also made a 45 minute food / loo / comfort stop for ourselves.
Can't comment on dog friendly hotels / motels because we did the Caen-Bordeaux-San Sebastian leg in a 33 foot Winnebago type motorhome. In our case, the San Sebastian-Granada leg had to be done in one day in a hire car because the M/H failed catastrophically and finished up on the back of a heavy recovery transporter for that leg.
The only other thing I would say is avoid Paris like the plague... route instead through Rouen, Le Mans, Tours, and Poitiers we didnt have to route that way because of our starting point at Caen...