Tip always book with the respective train company direct, Try re booking, Hartlepool Edinburgh return on Virgin East coats and Edinburgh Dalwhinnie return on Scott rail, Just done that on the respective websites with your dates and in come in for less than a £100. You might be able to get more off if you adjust you time of travel , Also if you are over 50 you can get a rail card from Scottrail and save even more. You will have to phone Scottrail to book a space for your bike.
Andy
ps,
Speak with Scottrail before booking tickets! restrictions might apply on early trains for bikes,