I have two dd, sometimes I want to talk about them together but make it clear that there are two of them - e.g. My dd1 & dd2 want to go ice skating. My dds want to go ice skating sounds too much like my ds who is particularly dear to me. It is even more confusing if talking about a friend with dss as that sounds as if she has one step son rather than two sons. I often end up saying 'my girls'. I have just posted to enquire about two different posters daughters and ended up saying 'your dd are'. I can't bring myself to add an apostrophe.