I generally don't offer alternatives, I only know the banana and yoghurt thing from DS sharing DH's food, DH allowed him to share, thinking that he'd already eaten his dinner, then DS ate the whole lot! (obviously I wasn't there at the time) if he says he wants something else I ask him what he wants, and I will allow him a small portion of something he chooses, to eat alongside his dinner, as this has helped in the past, although it's hit and miss now.
At school his teacher has to feed him otherwise he won't eat. At breakfast he happily eats banana smoothie by hisself (with a straw, I think that's why).
For meals I offer a mix of healthy foods that in the past he's said he liked, along with some others that he's not so keen on. but he won't even eat the stuff he supposedly likes. If he eats plenty of the healthy stuff I allow him a treat afterwards, a biscuit or yoghurt or whatever. I was wondering if it's something to do with jealousy of his younger brother...BUT...he will quite happily eat junk food without wanting to be fed. Chips crisps, chocolate, biscuits, you name it, no problem!!
He doesn't help out with food prep, he has no interest, unless it's junk food, and then only limited interest.