I love Lydia as a name, but unfortunately I can't disassociate it from a former colleague.
Swan - I love Freddie and Arthur. I wasn't sure about using a name with the first letter of another sibling. Same as I'm not sure about using a name with the first letter of our surname. I love Marian or Meredith for example, but not sure if I can get away with it. Probably outing myself out now!
I don't like any of your girls names with the exception of Isla. The problem with Isla IMO is that it's very much of the moment (in England at least) ie I think it will become dated quite quickly. Harriet and Robyn always seem to get a lot of love on here but they're not my taste. Louisa is very boring IMO.
I like all of your boys names except Evan. Henry is my next least favourite just because there are lots of them. Then again there are probably plenty of Samuels etc too!
I assume the spelling of Jayne is for family reasons? I much prefer simple Jane.
Girl Harriet Jayne- good name but not as sweet/ pretty as Alice. Elizabeth Jayne (Dh likes Beth. Me, not so much. I also don't like Liz/Lizzie)- v classic, v likely to get shortened so probably good to find a nn that you both like! Robyn Jayne- Robyn is a nice name but not in the same league as Alice, in my opinion. Louisa Jayne (would she be 'wheezer')?- Louisa is lovely Isla Jayne (Is it REALLY popular?)- like Robyn, perfectly nice name but not as classic and pretty as Alice.
Boy Samuel John- good Henry John- my favourite, love it. Evan John- not to my personal taste Elijah John- okay Isaac John- okay
I would associate other feminine classic names with Alice: Eleanor, Lucy/ Lucinda, Charlotte, Katharine, Isobel, Juliet, Celia, Beatrice, Susannah, Rose/ Rosalind. Boys-Edward, Oliver, George, Theodore, Quentin, Peter.