Offline/Deal with them yourself
You can't keep looking for excuses to ditch them or you'll never earn the adult's trust. You put yourself between the bickering siblings and they quickly shut up. You have their full attention.
"I don't want to have to send you back to your dad. Just be cool, okay? Can you both be cool?"
"I can be cool, but Beth's a loser!"
"That's not cool, Bray. I said be cool."
"Yeah Bray, he said be cool!" Beth sticks out her tongue at her brother.
You flick her exposed tongue. "That's not cool either. If y'all can't even pretend to be nice to each other, I'd rather spend my week doing chores. Got it?"
The two silently nod their heads. You might have actually gotten through to them, because they stay quiet for a good while after that. Then again, that success may be more due to how you managed to kill the mood for everyone. Everyone tries to make something happen for next several minutes, but it seems all the kids are afraid to do anything that might not be "cool". The awkwardness is only ended when you hear the lunch call off in the distance.
The aunts and uncles have all prepared an small assortment of munchables for everyone to fill up a plate. You manage to find a seat next to Nicole and try to make some small talk with her, though it's a bit difficult when you haven't seen her in years. Meanwhile, Wade goes off to sit with his family and the younger cousins are all still a bit sullen, but they slowly cheer up as their stomachs fill.
Your mom finds her opportunity to butt in on your business and stands behind you with her hands on your shoulders. "I'm so glad to see you all getting along so well! You know Justice, there's plenty of money to be made for a kid your age if you're this good with kids. I know plenty of moms with boys who would love to have a young man like you for their babysitter."
"They're just hungry. I'm sure they'll all turn into monsters again soon enough." you explain.
"Oh, don't sell yourself short." She seemed like she had something more to say, but got distracted by one of the baby cousins crying on the other side of the picnic area. "Since your cabinmates are all settled right now, do you think you could go see if Aunt Sara could use some help? Thank you so much, I know she'll appreciate it." Having found a way to dump more responsibility on you, she disappears.
Mom may not be watching, but you know she'll know if you don't do as she said and she'll come back again less friendly if you don't comply. Stuffing the last of your food in your face, you take care of your plate and follow the sound of screams to your next assignment. As you get closer, you realize it's not one but two crying babies, though one of them hardly like a baby except she's only wearing a diaper. The diaper isn't what truly shocks you though, because she is pushing aside her much younger sibling to get a turn with her mom's boob.
"Gem, you already got your lunch. It's Rocky's turn, now. No! There's no milk left it that one, remember?" The exasperated mother does her best to keep her child from exposing her other nipple.
You jump into the very strange situation the only way you can see how by pulling the child away and are rewarded by the mother letting her shirt fall open, fully exposing her breast to you. She may be your aunt, and not especially attractive, but boobs are boobs, even if they look a little chapped. You can't keep yourself from staring while you restrain the little one.
"Thanks, Jay. Did your mom send you over? I'll have to remember to thank her as well. I hate to ask anything more of you since I know you're watching over all the kid's in Wade's cabin already, but Gem here needs a new pullup. Would you mind terribly helping her out? Our cabin is the one right there. It's just pee."
Changing diapers has to be the worst kind of babysitting chore and unlike your mom, Aunt Sara seems like she would understand if you said no. Yet somehow that makes it harder to say no, not to mention she looks to be at her wits end, too tired to care about modesty. You also find it hard to say no to a woman baring her breasts. "Yeah, alright. I can take care of her."
Gem stops trying to get back to her mom once she understands you'll help her with her wet pullup, so you lead her by the hand back to the cabin. As soon as you open the door, she pulls down her pullup and runs naked to the bag she knows has her fresh ones in it. You grab one, unfold it and hold it out for her to step in, but she backs away and shakes her head.
"What, you don't want to put it on? That's why we're here."
She just stands there shaking her head and starts to groan.
"Alright, I can take you back out there naked if that's what you want." You grab her hand as if to lead her back outside.
"No!" she pulls her hand back from you.
Little kids are the worst. She looks old enough to start kindergarten, yet she's still wearing diapers and won't use her words. You're sure that by this age Emma wasn't even wetting the bed anymore and wouldn't shut up about anything and everything. This kid is definitely the worst if she has you wishing your sister were here instead. You'd even take Brayden and Beth over this. They may argue, but at least you know what it is they're upset about.
Gem only grows more frustrated standing there. She starts jumping in anger and whining wordlessly.
"If you don't want to go out there naked, then put your diaper on."
"Pullup!"
"Yeah, put your pullup on."
"No!" She looks around the room frantically and hums her frustration.
"What do you want?" You resist the urge to shake her little body.
She points at the bag you got her pullup from. "Wipe!"
Of course. She needs to be cleaned up before you put a clean diaper on her. You find the wet wipes and start cleaning her up. It would have been so much simpler if she could have just told you what she needed in the first place. She spreads her legs so you can clean her privates easier. Your cock jumps a little when you focus on her baby pussy. She's too young to really be that interesting, but she is a naked girl. Wiping her slit, making sure to get in all the grooves to clean her well, the thought occurs to you that if she really has that much trouble communicating, you could probably get away with taking quite a few liberties here and she wouldn't be able to tell on you. Then again, she may have just been nervous around you because you're basically a stranger and she's naked. As you consider your actions, you find yourself already stroking her slit without the wet wipe. She giggles at your touch.