My twins are 17 months, but because they were 12 weeks premature, they are developmentally equivalent to 14 months. I don't know if you carried your babies to term, but I know if they were even a few weeks early, you should go by their "adjusted age" (i.e. how old they would have been had they been carried full term) in terms of meeting developmental milestones.
Needless to say, with our rough start, I have been very much on the lookout for developmental delays in my twins. I can tell you that, at their current age of 14 months adjusted, Shane almost always responds when called by name while Dylan seems mostly oblivious. Shane started clapping around 12 months, Dylan followed around 13 months. They both understand the concept of waving, but they do it indiscriminately, which is often well after the person has entered or left the room. When it's just me, they will usually respond when I say "wave" or "hi" or "bye-bye", but if somebody else is actually coming or going, they usually freeze and give a blank stare. I believe this is because they are trying to understand the whole concept of people coming and going.
I must admit, this particular issue was causing me great concern last week after seeing Oprah's interview with Jenny McCarthy about her autistic son and the early detection signs that Jenny claims she missed (such as not responding to his name, flapping his arms, walking on tiptoes, spending long periods of time spinning wheels on toy cars or playing with door hinges, etc.). The startling statistics she quoted (one out of 94 boys will be diagnosed on the spectrum of autism), coupled with the fact that both of my boys at any given time have exhibited several of the above-mentioned behaviors, really got me going for a few days. I'm embarassed to admit that I became a little obsessed, at one point calling Dylan's name over and over many times throughout the day, not getting a response and worrying myself into quite a state.
Jenny also confirmed the story of other mothers that their babies were developing normally until about the age of two and then started to withdraw. This is terrifying and I find myself looking forward to reaching the two-year milestone and not having to worry about this any more. Those whose babies spent a long time in the NICU can likely relate to my heightened level of anxiety, having lived through the many ups and downs and watching my babies' hearts or breathing stop over and over again.
But, more recently, I have found great comfort in the exact thing you mentioned -- both of my boys are sociable, make eye contact, smile and interact with people. And, like you, I am reminded that all babies develop along different timelines, as evidenced by having twins and seeing the developmental differences between the two of them along the way. So...I've been letting go of my high level of concern and am feeling much better about it all.
Regarding your children's rejection of solids -- I was a little surprised by that. Like the PP, my boys also began insisting on self-feeding solids around 8 months. Due to circumstances too complicated to go into here, I breastfeed one and bottle-feed the other, but they definitely both show a strong interest in eating, eating, eating. I'm wondering if you are supplementing their diet with iron? My understanding is that the levels of iron (a really important nutrient for overall development) deplete in breastmilk after 6 months and need to be supplemented either dietarily or directly with iron drops or iron-fortified vitamins. So that might be a good idea until they start taking an interest in food.