Liferay's tomcat bundle, by default, is configured to take a maximum of 2.5G for the process, but it can run with far less - the default only recently was bumped up, because many people never change the default and then wonder why production systems run out of memory. For 1 concurrent user (the sole developer) on a machine, I guess that the previous default of 1G heap space is enough. Are you saying that that's too much for your developers' machines?
Having many developers on a shared server poses one problem: Yes, you may deploy different code from different machines, but: How about setting a breakpoint? Can you connect with multiple debuggers? If something fails, how do you know whos recent deployment caused the failure?
Sharing a server is an integration technique, not a development technique. If your developers don't have enough memory available for running their own Liferay server next to their IDE, it's a lot cheaper to upgrade their machines than to slow them down when everybody is accessing the same server and they can't properly debug. You pay the memory once, but your waiting developers by the hour.
Is it possible to share one server? Sure it is.
Is it possible to share one server without troubling each other? I doubt.
When you say: You think it's too heavy: What are you basing that assumption on? What does the actual developer machine look like and what keeps you from investing in the extra memory?
It's trivial to share some infrastructure - i.e. have all of them connect to the same database server (and give everyone their own schema). But just the extra effort and setup might require you to pay the developers by the hour as much as you'd otherwise pay for a couple of memory chips.
And yet another option is: Run Liferay on a remote server, but keep 1 instance per developer. This way you don't need the local memory, but can have the memory in the cloud. Calculate if you pay more for remote cloud machines than for local memory - that decision is up to you.
