[MMM]

R and L aren't "mixed" so much as they share the same sound, which is a sound in between the two. (Where on L you put your tongue at the tip of your top teeth, and R your tongue doesn't move...for the Japanese R/L sound your tongue taps the top back part of yor front teeth.

Japanese has fewer individual sounds than English names must be "morphed" to fit into the sounds available, and so they can be spelled using Japanese writing.

The "meaning" of an American name won't make any difference because foreign names are written in the katakana "alphabet" reserved for foreign names and loan-words, among other things. Only native Japanese get to use kanji in their names.