Fingers, dicks and toys all get different reactions from me, I can't speak for anyone else, but dicks are easier than fingers or toys, with toys being the more difficult... I don't know why, it just is what it is.
what Ms. Acon said.
My best advice would be to ignore any posts what so ever that mention child birth, because it's complete uneducated bollocks from people who read lots and understand little.
what Ms Acon said.
There is nothing "wrong" with using more than one, there is nothing "wrong" with just using one either... It all comes down to what she likes and how comfortable she is with more. It may well take more effort to use two, there may be some mental block saying "One is one, regardless of the size, two is more" which is stopping her from relaxing enough to easily take two... there could be countless reasons.
what Ms Acon said.
Take your time, and basically, if it doesn't feel like it's going in, don't push it... it'll be uncomfortable, it will probably hurt, and it'll fuck up any chances of you getting your dick in there later that night!