The picture is still not right.
Let me summarize some general rules.
1. Devas in the six realms and various Brahmas in 20 realms have things differently. They don’t have separate gandhabbas. They die with the same “body” that they are born with, i.e., there is one birth (jati) within that existence (bhava).
2. Humans and animals share a different mechanism. They can be born (jati) with dense physical bodies many times during that existence (bhava).
3. The rest of the realms are in the apayas, and can have either #1 or #2.
Let us focus on the mechanism for human/animal realms. That is what you are trying to model.
4. As an example, suppose a Deva exhausts the life in that realm and is born a human. When Deva disappears from the Deva realm, a human gandhabba appears in the human realm (at that moment).
5. That gandhabba may have a lifetime of many thousands of years. The lifetime of the human realm (human existence) is not fixed, unlike some Deva and Brahma realms.
– On the other hand, the lifetime of a physical human body is around 100 years.
– So, there can be many births with physical bodies for that human gandhabba.
– That is to say: there are multiple births (jati) for a given human/animal existence (bhava).
– There is only one birth (jati) for a Brahma/Deva existence (bhava).
– This point needs to be understood.
6. So, in the example of #4: Suppose the human gandhabba has a lifetime of 10,000 years.
– After born a human gandhabba, it may not be pulled into a womb for many years. Once getting into a womb, a baby will be born and that is a human birth (jati).
– Let me emphasize: Human gandhabba defines that human existence. It is the same gandhabba that will be born with different human PHYSICAL BODIES many times within that long time.
7. Therefore, when that first human physical body dies (let us say after 100 years), that gandhabba still has many more years to live. So, it will come out of that dead physical body and wait until pulled into another womb.
– That process will continue until the lifetime of that “human gandhabba” is exhausted after 10,000 years.
8. At that time (i.e., after 10,000 years), the “human gandhabba” will die. If it is inside a physical human body, then of course, that physical body will die too.
– That is when it will “grasp a new existence (bhava),” i.e., the cuti-patisandhi moment in the last citta vithi happens at that time.
– So, it could get into another existence (bhava) at that time.
9. There are a few exceptions to the above steps for a human gandhabba (#6 through #8):
– That human MAY commit an “anantariya (or anantarika) kamma” while in a physical human body (like us now). There are “good anantariya kamma” like attaining a magga phala or attaining a jhana. There are “bad anantariya kamma” like killing a parent or killing an Arahant.
– In either case, the physical human body can “bear” that new state arising due to the anantariya kamma. However, as soon as that physical body dies, the gandhabba state will die too, i.e., even if more time (of the 10,000-year lifetime) is left, that gandhabba will die and switch over to an existence dictated by the anantariya kamma.
– For example, if that human had attained the Anagami stage of magga phala, a Brahma in a realm appropriate for that Anagami stage will be born. If that human had attained a jhana, a Brahma in an appropriate Brahma realm would be born. If that human had killed a parent, then existence in an apaya would be grasped.
Let us make sure to get these “fundamentals” right. Please refer to the bullet number(s) and ask questions if not clear.
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