Sorry for the long message. Hope someone can help.
We have an older DS (age 6) who is diagnosed autistic. He's extremely clever, but has very high support needs at school due to sensory issues (and being very quirky/atypical for a six year old). His school is currently applying for an EHCP for him and he has a 1-to-1. The only signs were that he did his own thing during toddler group activities, was slow to toilet train, hand flapped, and had a slight speech delay.
His little brother (age 3) sailed through toilet training. He is already dry at night and was talking at 12 months. DS3 doesn't seem to have any social issues, socially copies constantly, is more keen on lying than DS6, and is a typical 'loveable' second child.
HOWEVER, he is a dramatically pickier eater than his brother at the same age, mostly that things are 'too slimy', 'too hot' or 'too wet'. He has problems with transitions to the point of fighting us to avoid putting on his shoes (even if he likes the activity he's about to do). He hand flaps like his old brother, lines up toys (his brother never did that) and is obsessed with vehicles (apparently normal for young DS, but his older brother has always had a wide range of interests. DS3's interests are steam trains, high-speed trains, cars, lorries, vans...).
Also, he does not sleep. On Friday night, he refused to sleep until 11pm. Yesterday night, he took off all his clothes at about 5pm (he especially hates socks, and screams if asked to wear them). Then, he refused to put on his pyjamas and fought me. I eventually got him into his bedroom, naked, at 8pm, with him screaming as though I was murdering him (he promptly fell asleep - the first time he's fallen asleep before 9:30pm for months now). He was awake again at 7:30am. This has been going on for months now and, to be honest, we are exhausted.
Obviously, with his brother being autistic, I'm wondering if he is also autistic. Everyone is telling me DS3 is entirely neurotypical, but I've also been told that the only sign that his older brother is autistic (if he's not in a sensory overload situation like a primary school) is that he runs backwards and forwards when excited.
DS3 and DS6 also get on like a house on fire. DS3 says DS6 is his 'best friend'. He copies everything DS6 does, including 'co-stimming' with him (i.e. running backwards and forwards). Everyone says he's merely socially copying, or he 'thinks it's a game' but he must get something out of this - or else he wouldn't do it. They play long complex games together, largely involving vehicles.
People who've seen them together, say their sibling relationship is entirely 'typical'. As I know that autism isn't a 'problem' with social communication, it's a difference, I keep wondering how neurotypical DS3 really is - given how well he plays with DS6.
Anyone have any experience of something similar? If so, did the younger sib turn out to be autistic?