Will it still look like them?

Yes, and the reason is a decision rather than a promise. The likeness is reconstructed from what is in the photograph and never restyled — faces are not smoothed, sharpened or corrected, because on a picture of a real person that is not an improvement.

The cost is that flaws survive. A soft photograph stays soft.

Why faces are left alone

Most tools that improve old photographs include face enhancement, and it is usually on by default. It produces a face that is cleaner, younger and subtly somebody else — the eyes get bigger, the skin evens out, an expression shifts.

On a stranger that is a nice effect. On a grandmother it is a stranger wearing her cardigan. The whole point of the object is that a family recognises the person in it, so that setting stays off.

Reconstructed, not invented

There is a real difference between recovering detail that is present but degraded, and predicting detail that plausibly should be there.

The first is what happens here. The second produces a print containing things the photograph never held — a pattern on a dress that was never that pattern, a building in the background that has acquired windows. Attractive, and not your photograph.

What that means you should expect

The result looks like the picture you sent, larger and clearer. It does not look like the picture was taken on a modern camera, because it was not.

Grain becomes less distracting. Edges firm up. Colour that has drifted comes back toward where it started. What does not happen is the photograph becoming sharper than the negative ever was.

Colour, and why it drifts

Old prints shift over time, and they shift in a direction — colour photographs from the seventies and eighties go warm and then magenta as one dye layer fails faster than the others. Black and white silvers at the edges.

Correcting that is recovery rather than invention, because the original values are inferable from what the fading did. What is not inferable is a colour the photograph never recorded, which is why a black and white picture stays black and white unless you ask for otherwise, and why asking for otherwise is a different request with a different answer.

Where it stops

Past a certain enlargement, faithful reconstruction runs out of material and the only way to fill the frame is invention. That is why size is tied to source quality rather than to price — the limits are covered in how big can you print an old photograph.

If the photograph is very poor, the honest answer is a smaller piece rather than a larger one with more guessing in it.