Welcome to the Great American RoadTrip Forum! Before you leave Twentynine Palms -- be sure to have a meal (breakfast) at the Cafe adjacent to the swimming pool at the 29 Palms Inn -- one of the best-kept dining secrets in California. April along the eastern Sierra is beautiful and so I would suggest heading north, past the Amboy Crater and the Amboy Shoe Tree and keep going more-or-less diagonally NE to Kelso (walk up the dunes if you are feeling like a walk...) and thence up to Baker and into Death Valley NP. Stay overnight at either the Furnace Creek Inn or Ranch and after exploring the park a little head NW on CA-190 to US-395 and head north.
Spend the second night at either Mammoth Lakes or Lake Tahoe and use US-50 to cross the mountains and turn south for Yosemite.
Mark