My DSis has 3 children, the older 2 have significant care needs and the youngest is a baby. All 3 still in nappies.
I have 2 children, both older than hers.
I never asked her to babysit and she never has.
I have looked after her older 2 numerous times, including when the others were born, long weekends so she could go away, hair and nail appointments and so on. Maybe once every 6 weeks or so, not all the time.
I have only had the baby once.
I reduced how often I looked after the children when she started expecting it rather than appreciating it and to be honest, I find the older 2 difficult to care for too now that they are bigger.
She and her husband don't work, the older 2 are in school full time and baby goes to nursery once or twice a week but my sister has started to complain that they never get any time off and needs a break. Her sister in law and my mum babysit and she also has a carer that they can pay to babysit.
My husband works full time and I work part time and study part time and our children do a few extracurricular activities so we don't have much free time.
Is it selfish of me to maintain that I don't want to babysit? Should I explain why? There is so much tension between us that I worry we will fall out soon.