#!/bin/bash
in=/a/b/c
li=/a/b/c/d/
g1=/a/s/t1/1.txt
g2=/a/s/t2/2.txt

for i in $(cat $li/ID1.txt); do
sed '1q;d' ${in}/${i}/${g1};
done > output1.xls

for i in $(cat $li/ID2.txt); do
sed '1q;d' ${in}/${i}/${g2};
done > output2.xls