[name_f]Helen[/name_f] or [name_f]Helena[/name_f]?
[name_m]Malcolm[/name_m]
[name_f]Alice[/name_f] or ?
[name_u]Dexter[/name_u] (twin of [name_m]Kristof[/name_m]/[name_m]Krister[/name_m])
[name_m]Krister[/name_m]/[name_m]Kristof[/name_m] [name_m]Atlas[/name_m] (twin of [name_u]Dexter[/name_u])
[name_f]Ivana[/name_f]/[name_f]Iris[/name_f]
Do Dexter and Krister sound too close to be twins?
I need help with middle names too. I want to somehow keep a theme with the middle name [name_m]Atlas[/name_m].
Last name is Jennerjohn.
Also welcome to suggestions on [name_f]Alice[/name_f] or [name_f]Helen[/name_f].
I like [name_f]Helena[/name_f] better but [name_f]Helen[/name_f] fits the rest of the names more
[name_f]Alice[/name_f] or [name_f]Amelia[/name_f], [name_f]Clara[/name_f], [name_f]Charlotte[/name_f], [name_f]Beatrice[/name_f], [name_f]Violet[/name_f], [name_f]Cora[/name_f], [name_u]Ruby[/name_u], [name_u]Clare[/name_u]
[name_m]Krister[/name_m] is too similar [name_m]Kristof[/name_m] works better
[name_f]Ivana[/name_f]
to keep the same theme with [name_m]Atlas[/name_m] you could use Greek names, mythology names, or place names/direction names.
[name_m]Apollo[/name_m]
[name_f]Athena[/name_f]
[name_f]Rhea[/name_f]
Kronos
[name_u]Demeter[/name_u]
[name_m]Hermes[/name_m]
[name_f]China[/name_f]
[name_f]Ireland[/name_f]
[name_m]Caspian[/name_m]
[name_u]North[/name_u]
[name_u]West[/name_u] etc.
I was going to reply but everything @melancholymusic said I completely agree with or like better than what I was going to say! Listen to her!! 
I love [name_m]Krister[/name_m] and [name_u]Dexter[/name_u] as twins. [name_f]Helena[/name_f] and [name_f]Ivana[/name_f] definitely sound like sisters. [name_f]Alice[/name_f] is beautiful but it doesn’t quite match up with your other names. [name_f]Alice[/name_f] might work better as [name_f]Adeline[/name_f], [name_f]Senna[/name_f] (shares the ‘na’ sound with her sisters name’s), or [name_f]Clio[/name_f]. The suggestion to use Greek/mythology names is brilliant. From there you could even pick only names starting with ‘a’ ([name_m]Apollo[/name_m], [name_f]Athena[/name_f], [name_u]Artemis[/name_u], [name_f]Aphrodite[/name_f], [name_m]Ares[/name_m], [name_m]Adonis[/name_m], [name_f]Atalanta[/name_f], and of course [name_m]Atlas[/name_m]).
Good luck with your final decisions!
I like [name_m]Kristoff[/name_m] and [name_u]Dexter[/name_u] nn [name_m]Dex[/name_m], and [name_f]Helena[/name_f] sounds good as does [name_f]Iris[/name_f], and I like [name_f]Alice[/name_f], but if you don’t think it’ll work, you could do something like [name_f]Bianca[/name_f] or whatever you look up and see if it works.