I will just add a few notes in case anyone searches and has this problem.
The umount command does not work because the filesystems are busy. You can try lsof but since you logged in as a user /home will always be busy. There is not way to boot to single user mode and have console access that I know of.
My insecure work around was to allow root to ssh onto the machine because it's home dir is on / instead /home which is part of the lvm you are trying to extend.
man/google/duckduckgo root login access
vi /etc/ssh/sshd_config
PermitRootLogin yes
AllowUsers Sean root
restart sshd or reboot
After you umount the two file systems in the instruction; the rest instructions they supplied work.
