Ok, since nobody else bothers I'll bite...

I'm not sure about the GUI tools but at least with on the command line and using a text editor you can accomplish what you are asking for here.
HOWEVER, I don't think either of them is a good idea. Sharing home directories
can/will cause problems if both users use the same applications at the same time since most apps store individual settings in the users home directory.
You could add a new user and then copy the old users home recursively to the new user, perhaps like this:

Code:
su

cd /home/newuser
cp -R ../olduser/* .
chown -R newuser *
exit
Note that this does not touch files or directories directly in /home/newuser whose name begins with a "." Usually that is a good thing since they often contain settings unique for that user.

Issue #2:
Giving all users write access is almost never a good idea since there are other than "real" users in the system that don't need write access to something like that (and giving them access can weaken security).
What you should do is create a group containing the users you want to give write access to the common directory, for instance by adding a line like this to /etc/group:
Code:
ducks:*:12342:hewey,dewey,lewey
(make sure that the number 12342 isn't already used in the /etc/group file, if so you need to pick another one that isn't taken)
Then you can create a shared directory for that group, you can put it almost anywhere you like:
Code:
su
cd /somewhere
mkdir shared_dir
chgrp ducks shared_dir
chmod 2775 shared_dir
exit
(assuming that /somewhere already existed and everyone or at least the ducks already had read- and execute-rights to it, write rights aren't required)
After that Donald's three nephews all have write access to /somewhere/shared_dir, including any subdirectories any of them have created there.