I've had a rather successful couple of seasons with Manchester United, so I'll guide you through this. Don't sell anyone until August, first and foremost. Around the 2nd week of August, offer Hernandez for 35M+ (if he's had a decent pre-season). Usually, Madrid will negotiate it down to around 30, or might straight agree. Rooney will get you the same offers, but the only difference is - he is stubborn and slightly loyal. He won't leave unless his salary demands are met.
I know you didn't ask for it, but I'll tell you this - Sell Rooney off after 1 or 2 seasons, even if he is a good goal getter. He'll be a burden on you if you don't, later on. Haven't been able to get him on a lower or equivalent contract or force him to accept other offers. No one wants to pay his salary. Might have to let him go on a free
If you need any help with your United save, feel free to approach.