It is certainly easier to have one person, especially for Health Care POA, as that is who the doctors will be dealing with in case of your incapacity. Likewise POA for financial affairs, it is a pain to go through all the different paperwork different banks require.
However, if Daughter and SO are friendly, on the same page as to your wishes, and you think it reasonable, put them both down. If you think it might be contentious, whew, I don't know what to say--either way there will be problems.
I am guardian for sister's kids in her and her DH's wills, I found it interesting that it is me only, and not my spouse, but it really makes sense, in case we were to split later. This is the only thing that maybe gives me pause about your SO and DD together. What if you split from SO and then don't get around to changing the forms?
Gotta love estate planning--full of the worst variety of what-ifs you can imagine!
Likewise Ha, it is wee bit distasteful when a friend of ours mentions he doesn't have to save for retirement, it is all taken care of when parents and grandparents go. ughh!