First things first...
I am planning a two week vacation in Spain, early Feb 2017 ( Feb 11 to Feb 25)
Start by being honest with yourself about how many actual, usable, full days you will have in Europe, not including your arrival or departure days. If Feb 11 and 25 are your travel days, then the bad news is that you really only have 11 or 12 real full usable days in Europe (you will probably leave on 2/11 and arrive on 2/12, on your arrival day you'll be wiped out from exhaustion, and the next day, your first full day in Europe you may be pretty jet-lagged....especially if managing kids through the whole experience).
Given how many (how few) days you have to use, your original plan (Barcelona, Valencia, Seville and Madrid) looks ambitious - not impossible, but somewhat ambitious (more on why below). Adding the Canary Islands in sounds crazy to me (you lose a day going to there from Spain and returning back to Spain, so subtract 2 more days from your already brief trip). Skip the Canary Islands, save that for a separate trip (the Canary Islands are interesting, but too far to include in this trip).
Before handing out my next bit of advice, a question or two: have you been to Europe before? (for that matter have you been to Spain before?)? I ask because... I think for most of us, your choice of 4 places in Spain includes an odd one and skips an (arguably) "better" place: Valencia may be a nice enough Spanish city, but on a first trip to Spain, I'd give it a pass. Madrid, Seville and Barcelona, yes, these are great places to include (although Barcelona is tricky - see below). If (as I'm guessing) you've never been to Spain before, and you want to see "the best of Spain" as most North American tourists would probably define that, I would spend those 11 days between Madrid, Seville, Andalucia (the region in the south of Spain), and other top sights in/around there. That includes Toledo (near Madrid) and, Granada, Cordoba (the great Moorish cities of Europe), maybe the White Hill Towns, and if wiggling your toes in some sand by the Mediterranean is important to you, a day or so at some beach town south of there.
I would advocate skipping Barcelona. Not because it isn't cool and worth seeing (it certainly is), but because it's a long way from the rest of "Spain" (the parts most tourists want to see). Take a look at a map of Spain. Barcelona actually works as well a side-trip trip from southern France as it does from "Spain." To maximize your time being somewhere (rather than going between places) consider sticking to Madrid, Seville, Andalucia, and the towns/cities/regions nearby. There is plenty of great stuff to see there and 11 or 12 days will barely scratch the surface and give you a taste of that.
Hope that helps.