First, let me advise you never to use a wide angle lens for a baby picture. The foreshortening of a 28mm focal length lens will be sure to (1) make the baby’s nose appear larger, (2) reduce the size of their ears to looking smaller and out of shape, and (3) probably cause an overexposure of the image due to the closeness of the flash to the subject. One the other hand, a short telephoto lens (100mm) will reproduce our angel’s features to a normal proportion, all of his (or her) different parts presented in the proper ratio. Even a small distortion of proportion has a definite (and detrimental) effect on the features.
While I’m not excluding taking pictures at night with a flash, I am recommending that you wait for daytime for that wonderful light coming from your window. Turn off the flash or cover it with two layers of white handkerchief. A setting of 200 ISO should be sufficient for a good exposure. The bottom pane is the one with the most photogenic light, so if you can, close off the upper part. Try raising the mattress in the crib so that you can see the baby without looking down. Soft light from the sky or light reflected off clouds produces a three dimensional rounded effect especially flattering to a baby’s face. If the room is furnished in dark colors, place a reflecting surface near the baby to fill in the shadow. Use a tripod or other support and shoot away.
Try different angles: a high angle looking down, a position on the opposite side of the crib (turn it around), or even through the bars. Avoid using the macro setting on a zoom lens, since this setting most often incorporates a wide angle focal length. Find the closest distance possible on your short telephoto lens (85mm – 120mm) and stand at that distance. A two diopter close-up attachment lens could halve this distance for super close-ups.
For twins, try to have one sit and one stand. The diagonals produced in the composition introduce a dynamic note to the picture. Important is to have all eyes pointing in the same direction. A squeeze toy helps.