Using GNU sponge to do in-place editing of file1.txt:
{ cat person1.txt; tail -n +8 file1.txt; } | sponge file1.txt
This concatenates the person1.txt file with all but the 7 first lines from the file1.txt file and saves the result into file1.txt.
With sed, you would do the same with
sed -e '1r person1.txt' -e '1,7d' file1.txt | sponge file1.txt
(you could use 8,$!d in place of 1,7d), or, if using GNU sed,
sed -i -e '1r person1.txt' -e '1,7d' file1.txt
This inserts the contents of person1.txt at the start and then skips the first seven lines from the file1.txt input file.