YANBU
Your parents are BU, op, not you.
It seems very mean & selfish of them from where I'm standing. For me the whole Christian, working for the church thing whilst turning their back on their DD & DGS issue would compound my frustration & upset.
Telling you that you are amazing won't help, but I think you are.
Here's why:
Being a single parent is extremely tough.
Heap on your the stresses of your job.
People don't realise that a mixture of day & night shifts is much more exhausting (physically & mentally) than doing either night shifts or day shifts.
Your son has additional needs.....
To all the haters - I'd love to see how many of you could spend a week in the OP's shoes.
I would approach the church. Do they have a church newsletter or magazine for notices? I would put a request in, worded very carefully eg.
A single parent in the parish is struggling to cope with work commitments and childcare for her 11 year old son with autism. In return for ......(eg running errands/an afternoon of HW per week/an evening meal being cooked,) she wonders if there is anyone who could offer support to her from the hours of ......one day a week.
This might be a ridiculous idea, I don't know.
Maybe your best bet is to advertise at the local college for people doing childcare courses as other Pps have said.
Wishing you all the best, OP. 