You’re main pluggin can use register_activation_hook and use the function you register thru the hook to activate you’re necesary pluggins.
Smth along these lines :
// get already activated plugins
$plugins = get_option('active_plugins');
$puginsToActiv = array('Plugin1', 'Plugin2', 'Plugin3');
if($plugins)
{
$changed = false;
foreach ($puginsTostActiv as $plugin)
{
if (!in_array($plugin, $plugins))
{
$changed = true;
array_push($plugins,$plugin);
}
}
if ( $changed )
update_option('active_plugins',$plugins);
}
// code not tested