I have a small solution that helps with what you specifically asked, but I would hesitate to use it unless you are sure you do not want to try and build a better relationship with your neighbours.
The next time they are having a loud conversation right outside your window/at their front door clear your throat loud enough that it will interrupt their conversation.
I will give some explanation since I know it sounds like a very awkward solution. The main reason I suggest it is because although it makes interactions with those neighbours potentially more weird, you mentioned that you were not too interested in becoming friends, and doing it accomplishes all of your goals very efficiently, which are:
Do not make your neighbours mad at you
Decrease the amount and loudness of their conversations at the front door
This helps with 1. as clearing your throat is a known gesture for politely alerting someone of your presence and in your situation, although it does interrupt their conversation with incredible awkwardness, it leaves the possibility open that you think they simply did not know you could hear them, and will happily move the conversation elsewhere. Implying that someone has good intentions is a great way of deterring bad ones, without accusing them which would risk them getting defensive/mad.
This also helps with 2. in decreasing the loudness in a few different ways. First, now that they know you can hear them at the door they may try to do the right thing out of respect and a mutual desire to get along. Second, it interrupts that immediate conversation and turns it cold. The sudden awkward interruption with the implied indication that they have woken somebody up or that an unseen stranger can hear your private conversation should stop just about anybody in their tracks. Lastly, it deters future conversations as they will naturally desire to avoid such an awkward moment in the future, and probably go to fair lengths to avoid "avoid waking up the neighbour".
(Edit: This is not just a one off and I honestly can not see a situation where your neighbours would be oblivious enough not to associate it with a repeated problem. If they don't however, repeating the same solution of clearing your throat to interrupt their conversation should form a pattern.)
Doing this is somewhat rude/weird I know, but it solves your specified problem so I hope that it helps however it can.