What group photo are you talking about?
Also, what does character interaction/relationships have anything to do with the order of release? A character's in-universe connection with another character doesn't seem like as good a reason for their order of release their real-world popularity; didn't the fan poll for returning characters have NiCO forst then Tina, Mila, Christie and Lisa and Rachel last?
Rachel and Lisa being added in next year makes more sense simply since they each placed last in different character poll; Lisa was in the initial DOAX3 poll and Rachel was last more recently.
Okay, when you boot up the game, when it gets to the title screens, they have these group photo thingies, one for three girls each. Here's some examples:
Kasumi, Ayane, Luna:
Nyotengu, Honoka, and Marie Rose:
Kokoro, Helena, Tamaki:
Momiji, Hitomi, Leifang:
Misaki, Nagisa, Fiona:
Kanna, Monica, Sayuri:
Patty, Tsukushi, Lobelia:
Nanami, Elise, and Koharu:
That's what I'm referring to. And in the case of the first four images as well as the last one, they directly referenced event episodes with all of them together (the first four referenced specific episodes featuring them in the first anniversary, the last one referenced one of Koharu's debut event episodes).
As far as Lisa and Rachel, the problem is that they'd need to make sure Lisa's out of the way for the Xtreme Beach Volleyball anniversary event (which is going to be in March 2023), and aside from that, Lisa was ranked last in the DOAX3 poll (well, either her or Christie). That would mean they'd need to release Lisa or Rachel first after Mila, then have Christie be in-between. Especially if we assume that they're going to release them in a couple of months (very quickly in other words), based on Tina's development, which unlike the other girls we know EXACTLY when she started development due to their leaving a paper trail.
As far as NiCO is concerned, we shouldn't forget that the girls are most likely going to be released to tie directly to anniversaries for their respective games since they're close together. Meaning we're most likely going to get Mila first after Tina (since DOA5's anniversary will be occurring real soon), followed by Lisa most likely (DOAXBV is most likely coming in soon, and aside from that, she's connected to Tina and Mila. They had Leifang paired up with Hitomi and Momiji when they could have just as easily paired her up with Luna and Tamaki. I'm doubtful she's going to be paired up with characters she hasn't had any direct connections to). Christie will probably be inserted next after her, since she tied with Lisa recently, and aside from that, DOA3's anniversary's this year in fact. Rachel will probably be after Christie, due the upcoming Ninja Gaiden anniversary in October of next year. Finally, for NiCO, she's most likely going to be released mid-to-late 2023 since that's around the time DOA6's 5th year anniversary is going to be held. Don't forget, the primary reason behind Tina being released at all was that DOA's 25th anniversary occurred around the same time. Most likely the other girls are also going to be released to promote their respective debut games' anniversaries.