The meaning of the dream depends on what the trigger was. I do not know what it was so I am interpreting it in a general sense.
Grandfathers sometimes symbolize the older generation. They also symbolize the wiser generation because of their wisdom, sometimes symbolized by their gray hair or beards, or mustaches.
The fact that he sits on the front porches suggests that he is looking at the future or his mind is on the future.
What is actually in front of him in that front yard (the present and the future) is not good. The broken and crashed vehicles stacked on each other speaks of people’s jobs, or ministries, or life motivations being in a bad state or a bad condition. It speaks of dreams and visions desires broken and destroyed. The 2 trees that were fallen over even speak of people who died (literally and or spiritually) because of the struggles and the dissension and conflict that they endured.
The fact that you saw this through the window speaks of you enjoying the ability or opportunity to have spiritual insight into this situation.
It appears that you adored your grandfather, at least you did in the dream, and him there on the porch is something that you wanted to capture forever so that you can remember what he stood for and what he achieved or whatever he shared to shape the future. Unfortunately, whilst you were looking at the past (your grandfather) you saw that even the wiser and older generation had their troubles. He ate bad food (bad words) (see the meaning of “food” in the dictionary) (I suspect that the bad food is bad doctrines and lies), and that bad food made them sick, that is why he vomited on the porch. Unfortunately, the little girl in the future (the new generation) still has the same problem. They still eat bad food and it makes them sick as well.
You played a positive role in the dream. You were chosen to help the new generation not to make the mistakes that the older ones did. It is clear by the warnings that you gave her. You showed her the devastation (things that happen when people make wrong choices and eat the wrong food), and you told her to stay away from certain vehicles (probably ministries and bad motivation).
The girl’s mother probably speaks of the existing generation, who is also sick (like the past (grandfather) and the new (girl) and the generation who does not exist yet (invisible granddaughter) is going to be).
I suspect that the part of people who discussed events which took place in other countries, speaks of bad things that may spill over to them. Usually, “strangers” and “unknown countries” in dreams speak of people or countries that cannot be trusted. So these people were concerned about the way things progressed or the latest events and incidents that they heard about.
Your invisible granddaughter speaks of even a later generation, who does not even exist yet, will even be worse. The rebellion is apparent (the taunting and the lesbian) and the fact that the pastor could not do anything, speaks of the inability of the church to help or to change people.
The “And I said to her no matter what you say, you know in your heart that this is not who you are”, speaks of you willing to do what you can to influence the church and the body of Christ in a positive way. Too many people are so dismayed and disappointed about what they see and experience in the church, so much that they decided to give up and let everything go its course. This is not want God wants. He wants us to do what He has sent us out to do (the great commission).
We can change the ways of the future generations just as we can the existing and the new.
So, in a general sense, this is what I see in this dream. Of course, if another trigger is revealed, then the meaning of the dream will change according to whatever the trigger was.