The arrangement works well for everyone, although Dean is perhaps the slowest to accept it. He was always a little more suspicious of others than his brother, and under the influence of the Mark of Cain he was even more slow to trust. Castiel just seems happy at having another angel around in general, though he still comes and goes, working on his own projects as well. Sariel heals from her injuries, both those caused by the fall and other older ones and is willing to share information with the hunters and assist them. Sam finds himself enjoying the stories the angel shares, and as one of the oldest of them Sariel has many tales of history and much knowledge she can share.
For the most part the brothers leave the older angel back at the bunker when they go on hunts, having her look up information and just generally catalogue items in the inventory. Sariel finds this all rather boring but understands their reluctance to bring her along, so it's better than doing nothing. It is about 2 months before Sam asks if Sariel knows anything about the Mark of Cain.
Dean is out on a grocery run and Castiel is with him. Sam cautiously explains how the mark has changed his brother and wants to know what the ancient angel might know, specifically if a way exists to remove it.
Unfortunately, the information that Sariel has is either stuff they have already learned or simply not helpful. She shares that mark was used to contain God's sister, the darkness to his light, and that Lucifer was actually the first to have to bear it, something that surprised Sam but was not helpful in the long run. Like Death, Sariel informs Sam that the mark can't be removed without the Darkness becoming free again. Although she theorizes that it could be possible to remove the mark, Sariel does not know how nor does she think it to be a good idea.
It only a week later that an unexpected visitor returns to the bunker, when the Sam and Dean return after another successful hunt they find a familiar figure waiting outside the door. Still a little guilty over his previous actions, Dean allows Sam to take the lead.
"Gadreel?" questions Sam. "I thought you were going to travel?"
"I did, for some time," answers the ancient angel. "I have recently learned of some upsetting information, and I had hoped you may have something which can assist me in my new task."
"Uh, well, come in and we can talk about it?" the taller hunter offers.
Dean opens the door to the bunker and the three men enter, heading down to the war room. He notes that the angel still remains cautious around him, keeping Sam between them, and does feel a little bad about that. The older hunter offers to put their gear away and leaves the other two to talk.
"First, what 'task' are you working on?" asks Sam, remembering how easily the angel had been misled before.
"While traveling I learned that one of my siblings did not survive the fall," Gadreel shares, the grief obvious in his demeanor.
Dean returns, bringing with him some beers for everyone, although the angel seems more confused by the gesture.
"I'm sorry to hear that," Sam says earnestly. "How does that give you a task though?"
"I have not heard of my other siblings during my time here, and I wish to locate them. I have no one else I could ask for assistance, and had hoped you may be able to offer some support."
Something itches in the back of Sam's brain, as if he knows something about this but can't quite remember what. To the angel though, he admits that he's not sure what kind of support they can offer.
"It is fine," the angel allows. "I perhaps should not have come here, but I did not know where else to go."
"Tell us about them," Dean asks, trying to make a gesture of peace. "We can maybe keep an ear open, ask Cass if he knows anything."
"Ara, is a healer, prefers male vessels. He is kind to everyone, always willing to help. Aramiel does not like to fight, he is very much a pacifist," Gadreel describes his siblings. "And Sari prefers female vessels, I think…"
"Sari?" Dean interrupts. "Like, Sariel?"
The angel turns to look at him sharply, "Yes, you know of her?"
"Yeah, I'll be right back," Dean says absently, as he stands up and leaves the room.
Gadreel watched the older brother curiously, and while his brother his gone Sam encourages the angel to continue.
"Sariel is to me, I think, as your brother is to you," he continues. "She is the one to always look out for us, she kept the rest of us protected."
Shortly there is the sound of footsteps coming down the hall, and voices echoing ahead of their owners.
"What is so important, but you can not tell me?" the female voice questions.
"It's good. You'll like it, trust me," Dean's gravelly voice reaches them.
Dean leads the young woman into the room and gestures towards the male angel sitting at the table, "Ta-da."
The woman looks where Dean is pointing cautiously before freezing in shock. The blond man turns around and he too freezes temporarily, before he stands and the two beings approach each other. There is no hesitation as the two ancient angels embrace each other. It is a long time before they release each other, so long the brother's wonder if the angels even remember that they're there.
Finally the angels separate and sit across from the two hunters, both of them thanking the human siblings.
"We did nothing," Sam insists. "It was just lucky coincidence."
"Still, it is a start to regaining my family," Gadreel states, Sariel agrees next to him.
The humans temporarily leave the angels alone in the war room as they head to the kitchen to get some food. When they return they find the other siblings busy sharing their stories of what has happened to them since the fall.
When they are done talking, Gadreel turns to his sister and shares his plan find their remaining brother and asks if she wishes to join the search. Sariel is quick to agree, but than turns to Sam and Dean and states that she owes them a lot.
"It's fine," Sam smiles sincerely, "We totally get it. I'd do the same thing."
Dean agrees with him.
"If you need anything, well, I, uh. I can't fly," admits the female angel haltingly. "So, I wouldn't be good in an emergency. But if there's anything I can help with, just pray to one of us, yeah?"
"Sure, thanks," Sam accepts the offer.
The human brothers see the angelic siblings out and then head to their rooms to get some rest after their hunt. The angels begin to walk in the direction of the nearest city and discuss what their first move should be. They debate the pros and cons of praying to their brother and finally decide that this is the best way to search for him. Both send prayers out, aimed directly at Aramiel and eventually they receive a prayer back. All that remains is to set a location to meet.
It takes two weeks for the three siblings to finally meet, mostly slowed down by Sariel's inability to fly. They are all glad no one was able to listen in and they have their reunion uninterrupted in a public park. They share their stories of what has happened and what they have been up to in since they last met. Having missed each other they decide that they will spend their time together and explore the world that humans have created.