I like one. DP likes another. 3rd is ok for both

That's what I would do actually.

You: Tealy

DD: Tealy-Jones

New baby: Tealy-DPname.

It's the fairest way.

It's worth speaking to a solicitor about.

Chances of getting ex to allow any other names to DD is slim, he's very, erm, alpha! (Narcissistic) Sooo complicated.

If you applied for a court order, he would not get a choice.

You would be very very unlikely to get permission to CHANGE a surname - but adding yours to double-barrel = very likely to be approved, especially if your argument is that it would enable both siblings to share a surname link. This is the way you explain it to him too, if you wish to bother to be diplomatic. Not about you, about both siblings. He won't like it, but he's unlikely to be able to prevent it.

Erin is a great name but your current 3 names (although all great names) don't really go with the Erin vibe.

I would expect Erin to have a brother named:
Jude
Toby
Max
Evan
Cole
Myles
Joel
Aiden
Caleb
Ezra

Addressing the surname bit first, could you double barrel if you get married? Especially if you actually just add the new surname on the back without adding a dash. So your current one becomes a final middle name? That way you share a surname with both kids. Your daughter may wish to add to hers too but doesn't need to. Your second child will still share a name with both parents and possibly their sibling.

All your first names are good names for a boy. Personal preference is George but I think Harry and Jack are both great and none of them are likely to date particularly badly. Anecdotally there are more Jacks around in reception/year one but more Harrys around in years 5/6/7. Not many Georges. But that's just where we are!

Other alternatives would be Oscar, Max, Edward, James or Luke.

All three are perfectly nice in my opinion, the usual caveats about don't spell out anything with the initials apply of course 😂

If it were me I'd either go for the name you both like or just wait til he is born and you might think he suits one name more than another?

"Even if you marry, you aren't going to share a surname with this baby"

Isn't she? She might want to take his surname, basically she'll have to choose between sharing a surname with her oldest or her youngest.

Oh I see OP. Yes that makes it more difficult.

I really think that the first name choice should be yours, then. Even if you marry, you aren't going to share a surname with this baby - yes you should have first choice of the first name. Because - you say you 'can't' give the baby your surname... well, you could, legally. Because it's your name. And your daughter's name. Your DP should be very relieved that you aren't saying that the baby WILL have your own family surname, that it's more important that it shares with its own sibling and mother... especially after your last experience. He's very lucky. He should quit while ahead.

If you wanted to get a court order to add your own birth surname to your older DD's, you'd probably get permission. If you wanted to go down that route, you could think of double-barrelling or having your birth surname as a middle name for both.

What Yoni said. If baby has his surname he can't dictate the first name as well. Ideally you'd agree on a name you both like but if all else fails the mother should get the final say.

Anyway. Here are some boy's names I like, some more classic and/or popular than others. No idea if any will be to your taste.

Adam
Ethan
Ivo
Jacob / Jake
James
Leo
Levi
Max
Reuben
Toby
Zack

They’re all very popular, frequently used names. I probably prefer Jack of the three.

George!

Not to try and be disrespectful to what you say above by the way OP, it's a valid choice and your choice, BUT that really is usually the fair way this works - the recognition that the family name is being 'given' to his side of the family even though no marriage, and that he's then nice enough to be gracious about you choosing YOUR baby's first name. As logn as it's not something he hates!

Personally I like Harry best - I'm not a fan of George, but Jack really is completely boring and overused. It's a nothing name really.

But all of them are completely popular and inoffensive.

It isn't always black and white on surname choices, so I will respectfully say that I'd prefer to leave that conversation out of this thread.

So I'm guessing he's getting the surname even though you aren't married? In which case:

his choice of surname - your choice of first name

he wants the first name - then the surname is yours, as should be traditional.

Would that help resolve this?

They're all popular names so I wouldn't let jack being popular put you off. Harry and George are equally popular, possibly George more so with the recent burst after Prince George.

The Harry H depends on the surname, if it's different enough then not a problem but as a PP said Harry Harrison is a bit much, Harry Henderson is possibly a niche reference but not unknown.

I wouldn't get hung up on sibling names 'going' together either.

"Surname starts with H"

Whose surname? Yours, I hope. But probably his.

I really like the name Erin, it's unusual but not "out there". Your boy's names are quite dull in comparison, nothing wrong with any of them but they're nowhere near as nice. Anyway, if it must be one of those three, go for Harry as it's the one you both like.

I think George is very popular. What goes best with surname?

Harry.

Harry

Depending on what the H surname is.

George and Jack are quite samey in terms of popularity.

George is wonderful.

Jack and Harry are traditionally nicknames for John and Henry but I guess at this point they are used more and more just as names.

My preference:

George
Harry
Jack

All go with Erin.

H depends. If it's Henderson it's fine. If it's Harrison, not so much.

Keep thinking of other names, you might find a new one you both love!

Of the three I prefer Jack.