益 is your last name. It is an extremely rare last name, so I think you might be mistaken. It might be either 易 or 伊, both are more common last names with the same pronunciation (different tone).
瑞 means Lucky, fortunate.
萍 is a type of water grass. It doesn’t have a root and goes wherever water goes.
Both are commonly seen used in people’s names.
As Shizhe Di commented:
Chinese orphanages often give orphans a symbolic surname. In the past, unification was the “党” and “国”, but now it is more diverse. For example, as far as I know, the children in the Changzhou 常州 Orphanage are surnamed “Chang 常” or “Yu 虞”, while the children in Suzhou 苏州 are surnamed “Su 苏”. Therefore, Yiyang’s 益阳 orphan’s surname “Yi 益” is very reasonable.
In addition, as far as I know, when a foreign country adopts a Chinese orphan, the Chinese side will provide relevant Chinese documents, including the name in Chinese writing.