I hope everything works out for you with Oliver.
I'm a complete novice where Cockers are concerned but I do have a 17yr old son & know from experience that 17yr olds can be stubborn & so can parents (I certainly am!) & then you end up at loggerheads.
I think in addition to Ollie's training, a key thing to make this work will be keeping your Mum on side with you. Talk to her, ask her for help (we parents love it when our teens ask for help, makes us feel needed
), be completely open with her but in a non-confrontational way, let her know how much Oliver means to you & how important it is to you for this to work. You'll find that if you approach it the right way, your Mum can be your greatest ally.
Best of luck to you & Oliver.