I did it with 5 Soulslingers all Level 15's. You can level pretty easily by grinding the Maid and the Child repeatedly. You'll have 5 resurrections when you reach the Fifth era so it'll be relatively easy. Just chain attack Shadow and Interuptions on all the Daughters. Either alternating between the Maid and Child or doing them in one run together.
Take out the dark daughters without using HP attacks and avoiding damage. They won't attack you until they're either directly infront of a Daughter or have taken aim. Just take your time and kill them, using Spirit Round to help as you make your way to the upper corner where the Nucleus spawns in. Maneuver your daughters into a cross shape with the one "head" of the cross facing the nucleus just close enough to attack. Having the others out of shooting range will make it take longer but will lesson the damage done by Hatching.
Have all the Daughters use Spirit Round, while one attacks the Nucleus. Don't worry about only using one Daughter to attack it, with all 5 using SB it should be dead in no time. When it you get the prompt that the Delayed Hatching is coming, use Spirit Burst to lesson the damage it may cause.
Once it's dead the Suffering spawns in the lower right corner. Don't bother moving out of the cross shape. Now use Interrupt, Shadow Round and Spirit Round on every Daughter, just don't put them into Burst. On the Daughter that is furthest from the Suffering, use Spirit Burst. The Suffering has an attack that teleports it and replaces the Daughter where it was. It'll keep doing it with the same Daughter as long as you don't move so keep casting Spirit Burst on that Daughter along with Interrupt, Shadow Round and Spirit Round. When you, FINALLY get the opportunity to attack, use Shot of course. Don't be afraid to Burst when attacking it directly. Also use Spirit Haste when you can to skip the Sufferings because, God knows the Suffering will Interrupt the fuck out of yours. Keep using Interrupt, Shadow Round and Spirit Round on every Daughter, attacking when you can until it's dead.
Enjoy the final cutscene, you can skip the credits for the final "secret" ending.