We are going through something similar.
DS is nearly 14 months old and refuses point blank to hold his own bottle. He holds his sippy really well, but when I try to get him to hold his own bottle, he just gets really angry and starts pushing the bottle or throwing in at gets in a mood.
My guess is they will hold them when they are ready. I just think of it that I still get to have a cuddle with him while he is having his bottles.