I like [name_f]Collins[/name_f]! Not a fan of [name_m]Colin[/name_m] but somehow the S changes it 
In terms of spelling, I like the way [name_f]Collins[/name_f] [name_f]Wren[/name_f] looks [name_f][/name_f]- it looks more visually cohesive than [name_f]Kollins[/name_f]! I can imagine [name_f]Kollins[/name_f] working in other combos, just here C- looks best 
[name_f]Sarai[/name_f] [name_f]Collins[/name_f] is lovely too [name_f][/name_f]- and while I like [name_f]Sarai[/name_f] [name_f]Wren[/name_f] in theory, I trip on the Rs a little. (Sarai [name_f]Lark[/name_f], [name_f]Sarai[/name_f] [name_f]Lennon[/name_f], [name_f]Sarai[/name_f] McCall or [name_f]Sarai[/name_f] [name_m]Winslow[/name_m] came to mind as similar options!)