Betta Sorority Gone Wrong
I am brand new to this forum and am looking for some advice on a rather peculiar situation. This may be a bit long but I could really use some advice any and all is welcome.
I absolutely love bettas and have been keeping males for about the last 3 years. So I got this 10gallon tank from my sister (I don't know the brand or anything) but it has a hang on the back filter which seems to work pretty well and I got a heater and a lot of (fake) decorations for the tank. I then let that cycle after adding a quick start for about 6 weeks. So a few weeks ago I started doing research and found that you could keep a betta sorority in a 10g tank (I know a bigger tank is ideal). In research, I found that depending on who you ask you should keep between 3-6 bettas in a ten-gallon, heavily planted. So I went and got 4 (I meant to get 5 but there were only 4 within a 20 mi radius of my house). I got 1 koi, 2 dumbos, and a standard (at least that is how they were labeled). I read that it was best if they were as different as possible and the easiest way to do that was by getting all different types. So I brought these all back and did a bit more research on the best way to add them in and I found that you should add them about 15 minutes apart starting with the least aggressive one and that is what I tried to do. I watched them like a hawk for about 2 hours and saw some semi-aggressive behavior, but nothing that I wasn't expecting.
They were fine for about 3 days, and that is when I noticed that I wasn't seeing much of one of the dumbos, but I just thought she was hiding as the other ones were. The next day I saw the same dumbo female with about 1/2 of her fins torn off and the other dumbo with some slightly ripped fins as well. I promptly took out the very injured one and moved her to a 1.5-gallon tank I had on standby just in case and I added some API stress coat to help her fins heal. I then watched the tank for about 30 minutes and noticed that the koi female was being very very aggressive toward the other dumbo in particular, but also the standard, so I removed the koi and put her in the cup I got at the pet store (didn't have another empty tank). Within the next 5 minutes, the dumbo was completely terrorizing the standard so I removed both the other fish as well. Sorry, this is a long set up but I want to give as much detail as possible. I put paper towels in between the cups so they couldn't see each other because they were being very aggressive even through the cups. So with that, I went to eat dinner and when I came back the dumbo was no longer in her cup and she was nowhere to be found, the running assumption is that she made it onto the floor and was eaten by my dog (which is apparently fine for the dog).
So, to recap I now have 3 out of the original 4 bettas 2 in cups one in a small tank. I have another 5 gallons with a male betta right now so I would be willing to switch him to one of the other tanks, but I am really not sure what to do with all of these bettas. My local pet stores are apparently no longer accepting returns because of safety hazards so I am stuck with all of them for at least another few weeks.
Any advice on how to handle this? Do I try to keep them all separate? Do I get more females and try again? Also any advice on how to help my poor fish that is missing a large portion of her fins? It is a very strange situation and none of the research I have done has prepared me for this. I am no expert and haven't kept any fish other than bettas and guppies/mollies/platies.
Thank you for reading my long story, please give me some advice!