If DS has ADHD, is he on medication? Request a review of meds. If you suspect ASD as well as ADHD and GDD, has DS been referred for an ASD assessment?
How is DS’s sleep and eating?
Contact social care again. You need a review or even complete new assessments. Both for DS by the disabled children’s team and a carer’s assessment for you (and depending on what your own complex needs are, potentially an assessment of your own needs).
Appearing to manage at school but not at home isn’t uncommon. It can mean there are unmet needs at school. If DS is in SS, I presume he has an EHCP? Sounds like you need an early review. What support is DS currently receiving? Any help with his emotional literacy? Has DS had SALT and OT assessments and does he have ongoing input? Any MH support?
Have you had a home OT assessment to look at how the house can better meet DS’s needs and keep everyone safe?
Do you have sensory equipment at home DS can use? Some people find a trampoline &/or punch bag helps.
As difficult as it is, it sounds like DS needs closer supervision.
For DTD, is she known to the local young carers service? Sibs can also be helpful to speak to.
You may find The Explosive Child and The Out of Sync Child books helpful. Some people find Yvonne Newbold’s resources helpful. Some find PDA strategies helpful, too.