Since you asked for CC, I'll do my best to give that. I'll be the first to say that being thrown into portraits when you aren't expect it / don't want to do it really sucks. I've had it happen to me multiple times, and my best advice for this (and pretty much anything in life) is, "if you feel uncomfortable and / or don't want to do something, then don't." But now specifically to the images:
Im going to have to agree with PhotosGuy that the images do not look sharp. The first one looks especially soft, with the sharpest part appearing to be the front leg of the mom's jeans right below the knee. The second one looks in much better focus but I would not say it's "tack sharp". Based on your exif the combo you were using is definitely capable of producing stellar sharpness.
On the first image. The Pros: The composition is good. It appears you shot at about the mom's shoulder level and didn't cut off any body parts. The fence creates leading lines to the subject of the image. The Cons: The horizon on the image is slanted. If you had room you would have been better off scooting back to 200mm to add more compression and blow out the trash cans in the back. Is your niece pregnant? The way she is bent at the waste makes her stomach poke out in a slightly unflattering way if not pregnant. The baby appears to be falling backwards on the fence and I always try to avoid showing diapers on babies if possible. (Same as not showing underwear in a shoot unless that's what the shoot is about.) I think the contrast could use a significant bump and saturation could be increased a bit as well.
On the second image. The Pros: Again, pretty good composition. You got down to the proper level to shoot, and didn't cut off any body parts. The compression at 190mm is better in this one, and the fence behind is blown out very well. The horizon appears to be more straight and there is some pleasing bokeh balls in the background. The cons: The sun is in their eyes, causing mixed shadowy lighting on the faces and causing the mom to squint. There is a very easily cloned out spot on the mom's shirt. Again, I think the contrast could use a significant boost as well as the saturation could use a boost.
Unfortunately with children, you usually have to shoot A LOT to get good expressions from them. That's why I try to avoid doing family photos unless it's for people that I know.