Changing into an engineering major at UMD is subject to minimum grades and GPA followed by a competitive admission process (it appears that the minimum grades and GPA merely allow entering the competitive admission process, rather than assuring admission to the major, but ask directly to verify).
https://eng.umd.edu/transfer/internal
Note that since he was not admitted directly to the major, that means that those directly admitted had stronger high school credentials, so they may be tough competition in the grading curve in the beginning courses for the major that he needs to take and earn high grades in.
UMD grade distributions by course can be found here:
Going to Delaware with direct admission to chemical engineering is a lower risk choice if he is certain to want to major in chemical engineering.