I've never seen any kanji except 村上 for むらかみ.
so it should be the most common kanji in Japan.
as for ゆみこ, there's a lot of variations that could be such as 由美子、裕美子、祐美子、弓子、友実子...
I can tell you that 子 is always used for こ when it comes to Japanese girl's name ending with こ.
ex) 由紀子(Tsukiji)、幸子(sachiko)、恵子(keiko)、陽子(yoko) .. etc
hope it helps!