I won't add to what others have said so far regarding Jaspers training, it's all great advice, no less then you would expect from ST
What I would say though, I understand your frustrations and feeling you aren't giving Jasper what he needs, but I can assure you hand on heart, any thing you do today will in the future pay dividends, given time and effort Jasper will become as much part of your family as your children and just as precious to you.
IMO your biggest problem is bringing your family on board and uniting them as a team so you all work as one to train Jasper, everything you do with him must be consistent and every one must stick to the same rules, but always keep in mind that training is fun, every one has to enjoy it, not just Jasper.
I do think you will benefit from a one to one session with some one, just to start you off and show you how to train effectively, ideally with the whole family present, you need to be given confidence in your self to change Jasper and you need to be given confidence in Jasper that he is in fact a bright dog who wants to learn from you, generations of breeding have made him a a dog that is bright, willing and ready to do what you ask, it's inside him, he doesn't know that yet, you just have to coax it out of him

I would also suggest you keep a training diary, just write down each day or every few days how Jasper behaves, reacts and responds, it's boring and tedious doing it, but when you look back to the start and compare him to the present you will see clear progress, there will be days when you feel you've gone backwards, but on the whole you will see steady progress.
Most importantly, every one here is behind and waiting to help