I did this crossing in August and believe me the Sudanese are not at all s bad as the Egyptians, they are a regular pain in the ass in Egypt.
The crossing as you know goes on Wednesday and the car BArge goes on Thursday. YOu cant go with the cars on the barge and unfortunately there is no choice but to leave the keys with someone to drive the car onto the barge.
I used Midhat Mahir in Khartoum to help me sort some stuff there and his uncle, a guy called Magdi is the man on the ground in Wadi Halfa.
He can organise everything to get you on the ferry and get your car to Aswan safely. I have seen it work and you can trust them. They obviously will charge you but I dont think they are over expensive.
Midhats numbers in Khartoum are 00249912253484 or 002249121313101
Magdi's number in Wadi halfa is 002499 121730885 ( im alsmost sure but if its wrong midhat will give it to you)
best of luck
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