で、こんな感じかな？寝ぼけて書いてるんで自信なし。シフトJISの仕組み調べれ。
    while ((ch = fgetc(fp)) != EOF) {
        if( ch >= '0' && ch <= '9'){// 0 〜 9の処理
            continue;
        }
        if( CheckWordByte(ch) == 2 ){// 2byte文字のチェック
            char ch_low = fgetc(fp);
            if( ch_low == EOF )break;
            char wd[3];
            wd[0] = ch;
            wd[1] = ch_low;
            wd[2] = '\0';
            char* check_word[] = {"一","二","三","四","五","六","七","八","九"};
            for( int i = 0 ; i < 9 ; i++ ){
                if( strcmp( wd, check_word ) == 0 ){// 一 〜 九の処理
                    break;
                }
            }
            continue;
        }
    }