I have a 5525 and if I am correct the issue is simple and it is in gear. You can not start it with the power reverser in forward or reverse and that is what the "N" blinking is telling you to place it in neutral. It operates like an old stiff tur signal, have three positions. Up is forward, middle is neutral and down is reverse. Can not remember if it being in a range with cause this issue but be sure the power reverser switch is in the middle position and range lever and also the gear shift lever and believe that will solve the issue.
If I am correct on the power reverser lever don't kick yourself. Had a person who owns JD tell me my tractor had issue as he failed to crank it. He forgot to check that lever. Hey, also check pto lever for it will not crank if it is engaged. If it has the economy pto it has two levers, don't miss one is the speed selector. It is the other think longer lever that engages the pto.
They are blessed to have a friend who can help and is willing to help with all they have going on. May God bless your efforts and ease their hurts.