Khartoum is tropical desert, which usually does not ever reach freezing temperatures. There won't be much overlap of plants that grow in Washington state and also do well in Khartoum. The most likely choices for seed would be tropical plants that love heat and are used as annuals in the USA. things like Verbena species, Zinnia species, Marigolds, Amaranthus species, Petunias, etc could all grow in Sudan as long as they got water. Desert species from the lower Colorado desert that do well in Phoenix, Arizona could also be expected to do well. I'd suggest you go to the library and study the recommended plants from Sunset Western Garden Book Encyclopedia that are recommended for Sunset zone 13. Many true tropical plants would also grow well in Khartoum, but some tropicals won't take the high heat of summer if the nights don't cool off. I know this was a problem for some commonly seen plants in California desert areas like Palm Springs, where things like some Ficus species that thrived in Palm Springs would end up cooking in places like Rhiyaad, Saudi Arabia, which has a similar climate to Khartoum, because the summer nights stayed too hot.

You might be best to stick with annuals and vegetable varieties that may not be as available in Sudan. Are you sure there isn't a nursery industry in Khartoum that you could have your family check out to let you know what might not be readily available there, so would make more sense to import? I can say that the ornamental plant/nursery industry is actually fairly well developed in both Egypt and Saudi Arabia, but have no direct experience with Sudan.