I don’t seem to recall this correctly. Didn’t the sister and friends leave before belamu explained the ants and such? How did the friend know what they were then?
@TyUni @BanditHardon the reason why many didn't like the sister action is because without the plot armor. Their action could lead to a bigger mess and endangered everyone. Especially when the MC already has a plan with 90-100% success rate.
So its just plain stupidity without the plot armor that make sure they would be safe and the mc save them in the right time and place.
@loonacrunch: Well, raws are available until chapter 28, so you can check what happens (though based on the events, it seems that "im glad youre safe" part would probably not happen)