Tending to live animals, one doesn’t get any guarantees. Much less in the case of brooding, where every female is different, and every brooding attempt (from the same hen, sometimes) is different.
So far, I have only ever had successful broods in the bantam pen. That pen has multiple females of different ages, and most are related to eachother. They have always been cared for by a single male. All the females in that pen (with the exception of the youngest pullet) have gone broody, and have co-brooded and/or co-raised chicks.
The co-brooding and co-raising system seems to work very well here, with experienced hens and inexperienced hens raising batches together, as well as high ranking hens with low-ranking pullets raising chicks together. The males so far have been excellent fathers, looking after the chicks and imprinting quickly on them. The rest of the hens don’t seem to bother the chicks at all; a few reprimanding pecks are to be expected, but not a single hen has targeted the chicks here, even the overly mean head hen of the group. Even adult birds from other groups (back when the bantam group free ranged) never seemed to target the chicks, but rather fought with the mother.
No one can say for sure what will happen with your birds. I would trust your broodies to know what they are doing. If you see that things are not working out, either with the co-brooding/raising or with the rest of the group, then you should separate.
The chicks so far don’t seem to venture far from mum when in the nest. Staggered hatches are avoided, so the chicks almost never have more than a days age difference. If your hatch is staggered, it is likely that the hen(s) will abandon the nest in favour of their oldest chicks. This is where having co-broodies could help. Splitting duties is quite common with them.
If your girls are making it works so far, it is definitely a good sign. One won’t know for sure until the chicks are here, and possibly more active. Hopefully they all get along, as they do now.
As for the accessibility of your setup, pictures would really help. Chicks are tougher than we think, but we can’t know for sure how they’ll take to it, or how careful the mums will/can be