First of all, I'm sure if this is possible it is somewhere
in the knowledge base but I'm really not sure what to
search for to get the info. I tried searching for phone
line but couldn't get anything close to what I want to do.

Because of various restrictions with ICS and my inability
to work port mapping I want to try an unusual set up.

I have two computers, one has a connection to the phone
line (family computer) and one is connected via network
and isn't connected to a phone line (my computer). What I
want to do is dial up my internet account on my computer
but using the networked family computer's connection to
the phone line. Put simply, I want to use another
computer's phone line but the result needs to be that my
own computer is the one actually connected to the internet
and the computer whose phone line I'm using will be
connected to the internet via Internet Connection Sharing.

Is this possible in any way as it would save me a lot of
trouble? Any help or suggestions of where I could find
the info myself are welcome.

Thanks in advance,
Jeremy
p.s. further information about my set up can be supplied
if required.

Remote modem cannot be shared as you want, you'd better fix ICS.