“三个一幅”这种表述比较模糊笼统，不过根据可能的语境推测，以下几种常见英文表达供你参考：
Three pieces make up a set
“pieces”可以泛指画、照片、工艺品等物品，“make up a set”表示“组成一套、一组” 。例如：These three paintings make up a set and they look great hanging together.（这三幅画组成一组，挂在一起看起来很棒。）
A set consists of three pieces
“consist of”表示“由……组成”，此句强调一套包含三件物品。例如：A set of postcards consists of three pieces, each with a different famous landmark.（这套明信片由三张组成，每张上面都有一个不同的著名地标。）
Three items form a complete picture/effect
“form”有“形成、构成”的意思，“complete picture/effect”表示“完整的画面/效果”。例如：When arranged properly, these three decorative elements form a complete picture that enhances the room's ambiance.（当合理布置时，这三个装饰元素构成了一幅完整的画面，提升了房间的氛围。）