Who do we ask to do a reading?
Whoever you want. Sure, consider folks who you think will be comfortable speaking in front of others. But it is also an act of love to invite someone to be a part of your ceremony. So let that expression of caring trump how well you think someone will read.
Consider inviting folks from each side of the family to do a reading. Or choose a longer reading that can be split in half, with two people reading. Or, for adventurous folks, consider a back-and-forth reading between two people who take turns reading stanzas of a poem, for example. Certainly makes the experience more unusual and interesting!