my daughter was pretty stiff for the first 3 months, i thought she might be what Dr. Sears calls an "uncuddly baby." she also avoided eye contact, and even though she seemed content and didn't cry, she never truly seemed happy. i wasn't able to breastfeed, but she was worn and held all day, except for a few minutes here and there when she'd arch and scream until we put her on the floor or bed to play. it turns out it was her GERD (reflux) pain ... once we hit the exact right combo of meds and home methods (positioning, massage, etc.) she blossomed!! suddenly was very cuddly and loose, gazing into eyes, all that good stuff
anyway, before that, i was constantly worried i was a bad mama, more than just not being able to breastfeed. there were times when i thought all my cuddling her wasn't making any difference at all, she was so indifferent to it. i'm glad i stuck with it very persistently and didn't just sit her in a bouncy!!
what you described with the twins, i think it could most likely be the result of the detached parenting. but, it could also be a mild pain problem such as reflux ... constant pain for an adult becomes background static, but for a baby it is in the forefront. they don't cry out in surprise since it's constant, but they are unable to relax or truly become engaged in their environment.