Just a little tip, forcing people to interact with each other altho well intended, can end up REALLY bad.
My recommendation would be that, rather than forcing them to stay at spawn, give them the choice to, just incite them to be at spawn often, give them a reason to stay together but without forcing them.
That people have their own personal base away from spawn does not mean they'll never interact with others or that they can't also chose to play at spawn as well, by taking away that option, you're just gonna end up driving people away instead of forcing them to your will.