How many times can I extend my parent's visitor visa stay?

I am facing a very critical decision regarding my parent’s recent visit to the United States. My parents generally come and visit me every year. They stay here with me for 3-4 months and then leave to go back to India.

However, 2020 is not a usual year and COVID has forced them to stay longer than then need/want to. Given the situation, I had already applied for their stay extension in June for a visa expiring in July 2020. From what I researched, my understanding is that as far as an extension has been filed, it is OK not to wait for the response and assume approval. Which is what I assumed and they are still staying with me.

Now, the COVID situation is still not resolved and I feel like, IF Possible, I would like to extend their stay for another 6 months. However, though, I am a little skeptical on if it is strictly allowed. I have already filed for one extension and assumed its approval. I do not want to put their visual in a situation where their immigration status comes under scrutiny for unnecessary means.

So I do have two specific questions:

1. Is it possible to file for two visa extensions back to back? Especially in these circumstances?
2. How safe is is it for me to assume that the first one was in fact accepted even before I file for the second one since I have not got any official correspondence from USCIS on this yet?

I also understand that lately USCIS is understaffed and their website says that I should expect a delayed response. What I am worried about is what would happen if what I am assuming to be a delayed response turns out to be a delayed rejection?