Re: Can we have multiple master servers sharing the same repositories?
Unfortunately I'm afraid this won't work at all... the content in a distributed repository is signed by the ePO server that controls it, and the client machines are given the keys by the server that controls them - the clients will only accept content that they have the leys for. Additionally, distributed repositories are date/time stamped - so you'd have to be very careful about the order in which replications were done, otherwise you would wind up with one group of machines refusing to update from a distributed repository because they believe it to be out of date.
To the OP - can I ask exactly what you're trying to achieve? What's the reasoning for wanting to have separate servers? It may be that there's a simpler approach.