My son is 3 and my second son is almost 10M. Overall, I have to admit that Jacob has been awesome with his younger brother (Ryan). He shares toys, helps, gives hugs and even shares food (sometimes when we don't want him to, lol). I am so grateful for this. BUT, Jacob has regressed at times. Ryan will chew on his fingers or arm and Jacob will do the same. There are days when Jacob wants to be fed like Ryan or wants to drink from the bottle. I really think it's just normal. In our case, Jacob adores his brother and I think he mimics him to be just like him. I know that will turn around and Ryan will start wanting to act like his big brother. I kinda see it as a form of flattery to each other.
We are trying to potty-train - or at least are preparing for it - and I think that's part of our issue. He sees Ryan get a diaper change and whatnot, so he wants it.
So, what we try to do is to redirect Jacob. By this I mean if he wants to use Ryan's (smaller) sippy cup, I will get one of the big ones from the cabinet that look the same and I will tell him. "Ryan has the small one and Jacob has the big one." He loves that. I stress that Ryan is a baby and, like others have posted, I ask Jacob to 'help' teach Ryan. I explain that he is the Big Brother and he needs to show his Little Brother how to do things. It's really awesome to see him try and teach. Lol.
Some of the things I give into. If he wants me to spoon feed him a couple bites of food, so be it. But, I also have him feed me a bite or Dad. That way, it doesn't seem like it's an activity reserved just for Ryan. It makes dinner interesting sometimes. :)
I don't let him use the pacifier or bottle, though. I just tell him that Ryan has things that are his - just like he has things that are his own (his cars, books, etc).