I am expecting girl twins. I am considering naming one twin [name_f]Penelope[/name_f] [name_f]Therese[/name_f]. This is my moms first name & my [name_f]MIL[/name_f]'s frst name. I would have her go by the nickname [name_f]Lottie[/name_f], thinking of the end LA sound at the end of [name_f]Penelope[/name_f] & the T sound from the beginning of [name_f]Therese[/name_f].
[name_f]Do[/name_f] you think this is too far fetched?
It’s fine, I think. NN’s don’t have to make sense at all, and I think it’ quite clever.
It’s confusing. Have you considered using [name_f]Penelope[/name_f] and [name_f]Therese[/name_f] as middle names for each child (so the other baby doesn’t feel left out, and the first child gets an original first name)?
I think you can use whatever nn you want. [name_m]Even[/name_m] totally unrelated to the actual name on paper. It is somewhat related to the name you’re proposing, although very loosely.
rkrd has a point about dividing the names between the twins though… so they each have a person to honour. Unless you’ll give the other twin more family names / grandfathers?
Like the above said, you can use any nn you want. It doesn’t have to be related to their name at all, it’ll be a pleasant surprise to see a little girl go by [name_f]Lottie[/name_f] when her name isn’t [name_f]Charlotte[/name_f]. 
Yes, our first plan was to use our mothers names as middle names. The other twin will be named [name_f]Georgia[/name_f] which is my all time favorite girl name & a family name also. I have two boys so I have had [name_f]Georgia[/name_f] at the top of my girl list for 7 years now.
I also like the name [name_f]Evangeline[/name_f], however there seems to be a lot of [name_f]Eve[/name_f] variations right now so I dont want that as a first name.
Someone suggested [name_u]Nelly[/name_u] as a nickname to [name_f]Penelope[/name_f] which is how I came to think of [name_f]Lottie[/name_f]. I love [name_f]Lottie[/name_f] but I do not like [name_f]Charlotte[/name_f].
I think [name_f]Lottie[/name_f] works as a nickname. Heck, my kids’ nicknames are Stinkerbelly, Muffin and Bubsy. Not related to their names in any way, though I doubt they will carry over with their friends. If you like it, go with it!
I love [name_f]Georgia[/name_f] and [name_f]Penelope[/name_f] as a sibset! 
[name_f]Lovely[/name_f].
I think [name_f]Lottie[/name_f] for [name_f]Penelope[/name_f] totally works! If [name_f]Peggy[/name_f] works for [name_f]Marguerite[/name_f]… But actually [name_f]Lottie[/name_f] feels right as a nn for [name_f]Penelope[/name_f]. Kind of brilliant i think. [name_u]Love[/name_u] [name_f]Georgia[/name_f]!! I’m a twin with two other siblings as well! Congratulations!! And may the odds be ever in your favor…
[name_f]Penelope[/name_f] nn [name_f]Lottie[/name_f] honestly makes me cringe a bit, but I’m very traditional I guess when it comes to nicknames. To me [name_f]Penelope[/name_f] and [name_f]Lottie[/name_f] could easily be sisters so I have a hard time imagining one as a nn for the other. Also I think my accent makes it even more far fetched (LOH is a very different sound to LA so bare in mind it may only work locally for you).
But call her what you will, of course it’s your child so your name.