If everything is immaterial and just ideas like Berkeley states then how are ideas and experiences shared among minds to create our common reality? Does God just transmit these ideas to everyone's minds so they can then have an idea of God's ideas in Berkeley's understanding? I suppose we could take a solipsistic approach but if we assume other minds exist then do we too have to assume then there is a source outside ourselves for the ideas that compose reality that is commonly shared among us? Therefore, that's how consistency is maintained in this world, it's constantly being thought up and perceived by God?
There are many idealists, with many different answers to your question. The idea/matter interaction need not be simple, however -- after all matter-matter interaction is incredibly complex -- we have the whole set of physical sciences that have tried to understand it!
Theistic idealists have the option you described -- of assuming a God who manages communal perceptions to keep them mutually consistent. Not all take that approach.
Non-theistic idealists need some common substrate or field to integrate living thing's ideas, and then living thing's interactions would be with that field or its consequences. Many theistic idealists go with such a field as well. In many versions of idealism, the idealists use the material world itself as that integrator. The material world can be assumed to exist, but be malleable based on integrated expectations, or it can be a reflection or derivation from such a field.
There are other Idealisms besides Berkeley's but I will concentrate on Berkeley since the question centres on him.
Other minds - a crux in Berkeley's theory
Berkeley has little to say about our knowledge of other minds - specifically, about why he is entitled to suppose that there are other minds besides his own. God is an exception since Berkely is sure he can deduce the existence of God.
Knowledge of other minds poses special problems for Berkeley. Besides taking the bodies of other persons to be mere collections of ideas in my mind, he insisted that I cannot have any idea of the mind or spirit of another. For him, ideas are passive and inert and therefore totally inadequate to convey a likeness of an active being, spirit, or mind (Principles 21) Lacking ideas of minds, Berkeley supposed that I can still come to know of my own mind through a peculiar non-sensory capacity, which he called "inward feeling or reflection" (Principles 89), and that I can deduce the existence of God by reflecting that only a supremely wise and beneficent spirit could produce the variety, order and coherence exhibited in my ideas of reality (Principles 30). But while he prided himself on having provided a clearer and more certain proof of the existence of a divine spirit than any other in history (Dialogues II 212-213), he had little to say about why I should suppose that other minds than mine exist.
But he is not without resources:
The primary locus for Berkeley's views on other minds is Principles 145:
From what hath been said, it is plain that we cannot know the existence of other spirits, otherwise than by their operations, or the ideas by them excited in us. I perceive several motions, changes, and combinations of ideas, that inform me there are certain particular agents like my self, which accompany them, and concur in their production. Hence the knowledge I have of other spirits is not immediate, as is the knowledge of my ideas; but depending on the intervention of ideas, by me referred to agents or spirits distinct from my self, as effects or concomitant signs.
Argument from analogy?
No, for the following reasons:
It has frequently been maintained that the argument of this passage is one from analogy. Supposedly, Berkeley appeals to a certain resemblance be tween our ideas of our own bodies and our ideas of other bodies and from this he infers that other minds exist.2 But the argument for other minds that is contained in this passage is not an argument from analogy. Berkeley does not say that we infer the existence of other spirits from a resemblance between their bodies and our own body or even from a resemblance between their operations and our own operations. He simply says that we infer the existence of other spirits "from their operations." There are no premises affirming likeness or similarity or resemblance between these operations and any other. Berkeley does indeed note that these finite spirits, whose existence he infers, are "like myself." But this is stated as a conclusion, not as a premise.
Argument from causation
This appears to be Berkeley's main argument.
While Principles 145 and 148 do not appeal to analogy they do appeal to the cause-effect relation. In Principles 145 Berkeley refers to the ideas I have as "effects" which are "excited in us" by other spirits or "agents" which "concur in their production." And in Principles 148 these other spirits are described as "principles" of thought and motion. The idea is clearly that from the changes in my ideas - particularly those which I take to be expressions of thoughts or motions of a body - I go on to infer the existence of a particular cause responsible for those changes. This cause I then take to be another spirit, incidentally like myself. Another spirit because, as Berkeley frequently insists, spirit just is the only possible cause. And like myself because, presumably, the effects I witness are limited to the thoughts and emotions of some one animated body (hence the spirit is another finite spirit) and because these thoughts and motions evidence a degree of rationality (hence the spirit is another intelligent spirit). Thus, I infer the existence of other spirits, not from the resemblance of their bodies to my own, such resemblance being totally unnecessary, but "from their operations" - operations which, for Berkeley, reduce to alterations, motions and combinations of ideas.
(Lorne Falkenstein, 'Berkeley's Argument for Other Minds', History of Philosophy Quarterly, Vol. 7, No. 4 (Oct., 1990), pp. 431-440: 431-3.)