File Transfer over Internet

File Transfer over Internet

I am developing a Personal Assistance Program which lets me help my Family
Members and maybe Friends over the internet when they have trouble with
their Computer as they are non-tech.
I will be running the Server and Clients (Family Computers) will connect
to me. I have tried to make it as simple as possible by only allowing the
Client to Show a Chat window and nothing else. This is because they always
fail in doing anything I tell them so I have to do everything remotely.
Now I want to Implement File Transfer.I thought of using TCP/UDP but the
time and effort to code and test it are just too much for me.
Is there any other way which I can use to Transfer files over Internet?
Minimum Requirements:
1) It should be reliable
2) Resume Capability
3) Able to Transfer very large files > 1 gb
PS. It would also be nice If a Client could Transfer files to Other
client's directly as well such as Pictures/Movies etc.
Don't suggest me to use TeamViewer/LogMeIn/Join.me etc etc. It has it's
own problems as well and I want to code to do this myself so I can
implement extra features.