merge to upload and install

[aksana]

hi,
I have another question.
Recently Im the only one person who is working on modifying or adding a new module to the original one.
If I wanna work on with more than 2 people, how would you suggest what is the best way to merge modified files??
Adding a new field to Existing module automatically makes new table like opportunities_cstm.
How could I adjust those to another computer? through server??

To add a new module, not only adding a new module itself but also I have to modify some other module.
for example, vardefs.php in Accounts module is often modified by.

If two people(two computer) modify Accounts vardefs.php file, how can I merge vardefs.php to upload and install??

Does someone have any idea, if yes, could you please tell me??

thanks,
aksana