She’s not a SAHM in the traditional sense though is she, she’s a foster carer. She has perhaps 5/6 hours each weekday when the children are at school. Within this she has to attend regular meetings with her supervising social worker, regular meetings with the social workers of the 2 children, and attend training sessions. You say both children are very challenging so she may well be firefighting and responding to issues at school, attending SEN/EHCP reviews and/or meetings with school, dealing with consequential behaviour at home. She may need to request, attend, and chase up appointments with professionals involved with the children e.g. speech and language therapist, occupational therapist, paediatrician, consultant psychologist, educational psychologist, CAMHS, counsellors, Team Around the Family meetings etc and ensure any recommendations are communicated to and within school. Does she have to facilitate contact between the children and their birth relatives? Do the children truant from school or run away from home? Are her nights disturbed? Is she dealing with continence issues? Are the children violent to each other or her? Does she often have to repair or replace things? Source sensory clothing and equipment? Does she have to order and give out medication? Complete Disability Living Allowance applications etc? I’m not expecting a list of answers to these questions but pointing out that she is likely to have lots going on each day, which would explain why your house isn’t as clean as you’d like. It’s great you do stuff with the kids at the weekend but it sounds as though you think she should be using this down time to catch up on all the housework, when it might be the only chance she gets for some respite.
I don’t think anyone can advise if you’re being unreasonable in the absence of any real detail about what your wife’s life and typical day entails, but I suspect you’re not being entirely honest/or possibility even aware of the complexity of her job, and the effort required to effectively support 2 children coping with the trauma of whatever has occurred which means the state has decided they are unable to live with the families they were born to.
Can you arrange a chat together and without presenting her with a list of grievances about household chores you’ve done which you think she should have taken care of, approach it as seeing what could change to improve life for you all e.g. if funds allow, having a cleaner/gardener/decorater etc.