She doesn't sound like a bad dog at all, and I'm sure, deep down, you know that really. The vast majority of her behaviour is because her needs aren't being met somewhere along the line. That's not necessarily your fault - dogs are hard work and it can take a while to realise what makes yours "tick".
She is so so strong that my kids can’t walk her. She has pulled my mother in law over and she spent 5 days in hospital. (This lady is pretty strong)
All dogs will pull unless they're trained not to. I don't know what equipment you use on her, but I've found a Trixie Touring Harness really good - the D ring is very far down on their back and it seems to give me much more control. It's fantastic on my beagle, anyway. They're about £13 from Amazon if you want to try them out 
but the only real solution is training - I did the "stop and stand still" technique whenever he pulled, but another popular one is turning and walking in the opposite direction all the time. It means you don't get far at first, though 
I work just 8 hours a week, so I have time to walk her. She needs an hour in the morning and an hour in the evening otherwise she will destroy our house. I was prepared to walk a dog every day - come rain or sun, but her needs are excessive.
Two hours a day is pretty standard for most adult dogs and I don't think it's excessive in the slightest, tbh. It sounds like your expectations were perhaps a bit off? Walks don't need to be full on running around, a good, slow sniffy walk on the lead can be an excellent way to tire out a dog, and make sure you vary the route, time and location so she doesn't get bored.
If I leave her for so much as an hour she will poop on the house in protest.
It's not a protest - dogs aren't capable of that kind of thought. She's pooing because she's anxious and scared at being on her own. It's a bit like when humans feel nauseous and get a funny stomach when they're worried or upset. It's not her fault. If she has separation anxiety then you really need to address this with a behaviourist as it won't go away on it's own.
When let off the lead we have the exhaust her with a game of fetch otherwise she will not come back (we have invested a lot of time and money in training) we offer her roast chicken as a treat - she will only come back when she feels like it.
If her recall is dodgy then you MUST keep her on a lead at all times, for her own safety as much as anything else. You could attach a longline to her harness to give her some more freedom if you wanted - they're available on Amazon or eBay. A biothane one is best as it won't get weighed down, wet and filthy.
She scratches all our doors and destroys the kids toys if anything is left out.
The scratching sounds like separation anxiety and the toy thing is really down to environmental management. If she can't be trusted then everything has to be put away - it could cause a fatal blockage if she swallows something she shouldn't do.
She is not the dog I thought I was getting (relatively small) she is medium to large and just so unruly.
Cocker spaniels are not what I would describe as small - all the ones I walk and know are very much medium sized dogs. Crossing with a toy poodle is no guarantee of small offspring, sadly. Again, the unruliness is because her needs aren't being met - she's not a bad or unruly dog by nature, she just needs training and possibly a job to do.
She is aggressive with other dogs (never us and she is very sweet with the children)
Is she aggressive or a frustrated greeter, or lead reactive? It's very easy to mistake reactivity for aggression. But again, she must be on a lead for her own safety here. If she goes up to the wrong dogs and aggresses, she could end up bitten or worse.
The kids love her, we always thought we were against the idea of re homing but this is getting out of hand.
Please get help from a proper, accredited behaviourist. None of the problems you've listed are unsolvable - you just need to change your expectations (work with the dog you've got, not the one you want).
Good luck 