My close friend and I eventually fell out over this. She has 2 DCs, the younger one has very severe autism. The older one got used to missing out on a lot because of her brother's needs and mostly was OK with it. Days out would sometimes have to be cut short, holidays were difficult and she could never have a birthday party without him "spoiling" it.
No one wanted to play at her house because her DB would interfere and spoil their games and have a meltdown if he wasn't always included. If they did include him he would insist they played his way and my friend didn't intervene. So her friends stopped wanting to come around.
DF's marriage broke up, mainly due to her DH being unable to cope with DS's behaviour. As the DCs got older DF relied on her DD for childcare because she had to return to full time work. Her parents helped out as well but they found him difficult to deal with.
Things got worse when the DCs were 14 and 12. DF's parents said they could no longer have DS after school because of his behaviour. So DD had to hurry home from school to be there when the mini bus dropped DS off from his school. This meant she had to give up some much-loved after school activities. She became very resentful and there were constant rows. DD's schoolwork and friendships suffered.
In GCSE year the school offered after school revision classes and they strongly suggested that DD should attend because her grades had dropped alarmingly. DF said she couldn't attend because she had to look after DS. DF was angry with me because said I couldn't support her decision when she asked what I thought. I suggested she paid someone to look after DS until she got home but she didn't want to because money was tight.
DD scraped the necessary grades to get to sixth form and told her mother she was going to live with her father for her A levels if she had to continue to look after DS. DF found some paid child care. But the damage to their relationship was already done.
DD went as far away as possible to university and said she would never again live in the same town as her DM and DB because she "knew" she'd be expected to help out again and she felt she'd made enough sacrifices. Their relationship has never recovered even though years have passed and DD has 2 DCs of her own.
I love my DF but I feel she never really did enough to minimise the effect her DS's autism had on her DD. DD loved her DB when they were young and always helped him and included him in a lot. But her DM asked more of her than was fair.
Sorry for the essay. Some DCs cope well with having SN siblings and others don't. They should never be expected to have care responsibilities, imo.