it's very hard
We always struggled with balancing meeting DD1's needs (very high functioning autism)
and making time for younger NT DS1, who was very quiet and self-reliant,and tended to fade into the background. DD always resented any time we spent with DS,and DS became very self-effacing, and didn't think he should push for attention or affection.
DD1 & DS1 are now in their late teens. DD is much more emotionally aware, and comes across as a typical teenager,maybe a tad more self-absorbed and ditzy then average.
DS has grown into a teenage version of his younger self (quiet,studious child,but now with smelly socks and an x-box addiction). He doesn't feel he missed out when growing up,and doesn't resent DD.However, I still feel guilty that we went along with his compliant nature, and didn't find more time for him.
Now we have DS2 (moderate to severe autism) and (as far as we know)NT DD2;same 3 year age gap,same dynamic of very needy AS child with younger NT sibling,and the whole juggling act starts up again.I'm trying to avert previous mistakes by getting DS2 to help with and to play with DD2. We also have Sure start for me and DD while DS is at school.
At the weekend DP takes DS out for a walk/adventure/muck about in the playground while I spend time with DD. On Sundays we try to do something together as a family.I'm lucky to have DP's support. I struggled to look after the older two on my own,hindered by alcoholic ex-H. DP arrived on the scene when DD was 6.
Sorry about the huge, rambling, tangential post. What I'm trying to say is do your best, it generally works out ok, and any mistakes made won't be held against you.