I'm slowly, very very slowly working through this story here while I study kanji (using kanjidamage) and with basic Japanese grammar skills, very much a beginner.
間 seems to be leaning toward 'period of time'
However, this section suggest more like "intruding into a group" or something, like ones little brother trying to slowly make himself a part of you and your friends group of makebelieve super sentai band.
ある日を境に俺とヴィンスの間に混ざるようになったエミーは、木の枝を見つけてきては、勝ち気な青い目を長い金髪の間に覗かせながら、俺たちの間に入ってきた。
Is that true? Or is it still more like a period of time? Like a process or something? Also, how is it read? "Ma"? A furigana addon I downloaded puts "ma" over the 間, as does Google translate.