Itinerary Questions for 12 days in Summer

Day
1. ARRIVE Barcelona (3N)
2. Barcelona
3. Barcelona
4. Evening flight to Granada (2N)
5. Visit the Alhambra
6. Train to Seville (3N)
7. Seville
8. Seville
9. Train (via Cordoba for the Mezquita) to Madrid (3N)
10. Madrid
11. Day to Toledo
12. DEPART Madrid

We didn't have any problems with credit cards IN Spain. We have AMEX which isn't always accepted (even in the U.S.), VISA and Mastercard. When I was purchasing tickets online before the trip, some transactions seemed more successful with Mastercard. However when we were there, we never resorted to Mastercard (ours has a foreign transaction fee) You should check the details of your cards. I don't think you need a car at all for your trip. In Barcelona the metro and regional trains are easy to use. Personally with the number of days you have, I'd skip Madrid completely and fly from Barcelona to Sevilla or vice versa. Train is also good, tho takes longer. I'd add a day to Barcelona and a day to Sevilla with a plan to day trip to Cordoba. Other option would be 3 nights in Sevilla and 2 in Cordoba. Cell depends on which company you use. Some people buy local SIM cards. I chose not to, for one thing, I'd probably lose the other SIM card. I signed up for a plan with my carrier, Verizon, so that for $10 per 24 hour period I can use my phone internationally. Once you use the phone for calls or cell you get 24 hours from that point. No charge until you use it again. As it turned out, we never used the plan. Having wifi in the hotel was enough. We could email and receive messages and download any maps we needed when we had wifi and then just used the phone offline.

You didn't mention Granada in your plans. The Alhambra is a top Spanish tour attraction and is pretty amazing.

we are in Madrid at the moment, just went today to toledo for the day. we are spending 3 full days here in Madid ( which is easily enough) we caught the AVE fast train from Barcelona ( best way to go - 2.30 hours. book your tickets early for a good price) we spent 4 full days in Barcelona. ( which was enough for us)
as a guide, we have spent well over 6 months of previous european travel and our absolute stand out experiences this trip ( and our advice to any first time europe traveller) have been the sagrada familia ( barcelona) and the royal palace at madrid
http://www.patrimonionacional.es
if you don't see anything else in europe , then see these two. IMO the palace is SO much better than any other we have seen anywhere.
the trains are great, very easy and modern. but you may need to book through another web site than renfe ( do a search in the tab at the top of the screen- for advice)
with three people its probably cost affective to just catch taxis, they are EVERYWHERE, in Barcelona and Madrid. We have lost count of the amount of taxis we have used, but we did use the subway in barcelona. ( 4 of us) taxis worked out easier.
At the moment is cool ( read cold - approx 10-16C ) but with not many tourists. in the summer it would be totally different.
cards are used everywhere, if in doubt perhaps investigate a citibank card or similar?
BTW, our toledo day trip today was 'OK' (we have done a lot of travel - so it takes a lot to 'impress' us) if your time was limited I would skip it.
hope this helps.

Summer is extremely hot in southern Spain. The average high temperature (not the record high, the average high) in Seville for the months of July and August is 100F. Are you sure you're up for that? Europe is not as consistently air conditioned as the United States. Specifically, some museums, shops, cafes and restaurants are not air conditioned. Often the most practical way to escape from the heat is to return to your hotel room during the hottest part of the day, so be sure you choose well-located lodgings. And be sure they are air conditioned.

Madrid is not as hot as Seville, but it is also not likely to be a pleasant temperature during your timeframe. Barcelona tends to be milder but can be humid at times, which can make it not as nice as the posted temperature might suggest.

As for a car, one does not use a car in Europe for city sightseeing. It just doesn't work. Spain has extremely fast trains traveling between Barcelona, Madrid, Cordoba and Seville. They run much, much faster than you could drive. Trains to other major cities will probably be about as fast as driving and much less hassle.

Changing hotels takes time. It's not just the time you spend on the train (which as noted can be amazingly fast, given the distance involved). It's the time spent getting everybody packed up, fed, checked out of the hotel, and to the train station. Then at the end of the trip you need to get them to the new hotel, get checked in and settled. So when you say "1 or 2 nights" in Madrid, you are giving yourself either 1/2 day or 1-1/2 days in the city. Madrid is not may favorite place in Spain, but to go there for 1/2 day really makes no sense at all. Either skip it or give it more time.

Spain is a large country with many interesting destinations scattered all over. There are lots of places worth visiting, but none of us has time to see them all (even if we could agree on the priorities) during a single trip. So there are no "musts" for you to add to your itinerary. You and your family should get a guidebook and read about your options, or at least the ones that are near the places you are sure you want to go. I guarantee that you'll end up with more than twelve days' worth of sights, so you'll have to make the same sort of tough decisions the rest of us do.

Me, I'd take a look at the calendar and the historic weather data and stay in the north. Here's the August 2018 weather for Seville as reported by timeanddate.com.

Edited to add: Glenn and I have quite different tastes. I'm not a palace fan and the Palacio Real in Madrid was a couple hours of semi-boredom that I regret. And I loved Toledo. But I spent several nights there and I really like mudejar architecture. As I said above, we don't all agree on priorities.

• Any comments for our itinerary above? Are there any other places we must to see that missed above?
  Granada definitely.

• If we don't rent a car, is it easy to go for sighseeing by bus or subway?
  Public transport (metro & bus) is easy in Madrid and Barcelona. Sevilla and Granada are walkable.

• What's the best route to go between these four cities?
  Train is fast and frequent between major centres.

• Will the train be the best transportation to travel between the cities?
  Yes, except Granada where flying may save time.

• Can I use Canadian Visa or Mastercard there?
  Should be no problem.

• Do I need to buy local SIM card for my cell?
  Depends if you will have constant easy access to wifi.

• Should we fly in and out from the same city or multi cities?
  Yes, in to Madrid and out of Barcelona

Thanks guys for very helpful information!!
Do I need to purchase train tickets online before we go or we can buy tickets when we are there? Also the tickets for any attractions have to purchase in advance just skip the long line up at the gate?

I would suggest prepurchasing train tickets whenever it is feasible. You can save significant amounts of money. I never buy my first train ticket since it is always possible for a flight to be delayed. Sometimes for shorter routes with cheaper tickets I will wait to retain flexibility. For long expensive routes, I always prepurchase.

You have gotten lots of good advice/answers here but I suggest you read the many past posts on this subject under Spain. Much of what you asked has been already answered; but more than that, you will find answers to questions you haven’t thought of yet, as well as ideas for things to see and do that would interest your family.