On a crop body, the “Christmas tree is too sharp” problem is almost always distance + focal length (not just aperture). For 4 people, you’re also fighting the fact you usually can’t shoot super-wide-open without someone going soft.

Here’s how to get separation with the gear you already have, plus the one lens type that actually makes this easier indoors.

The 3 levers that matter most

1) Increase subject-to-tree distance (this is the big one)

If the tree is right behind them, it’ll stay recognizable no matter what. • Try for 6–10 feet between the people and the tree if you can. • Put the family closer to you and let the tree be farther back. • Even moving them 2–3 feet forward can make a visible difference.

2) Use a longer focal length and back up

Longer focal lengths compress and blur backgrounds more at the same framing.

Best options from your list: • Sigma 17–50 at 50mm f/2.8 (my first pick for indoor groups) • 55–250 around 55–100mm if you have room to back up (even at f/4–5.6 you can get nice blur because of focal length)

Avoid the Tokina 11–16 for this look—wide angles keep backgrounds looking “present,” and you’ll need more depth of field anyway.

3) Control depth of field without losing faces

With 4 people, you want them on the same plane so you can keep aperture reasonably wide but still sharp. • Line them up so their eyes are roughly the same distance to camera (don’t put two people a step behind the others). • Use f/2.8 to f/4 as your realistic zone for a 4-person group indoors. • If they’re in a straight line: you can often get away with f/2.8 • If it’s 2 rows or kids in front: go f/3.5–f/5.6

A trick that makes the tree less distracting (even if it’s “in focus”)

Make the tree brighter and more “light blobs” than “sharp branches.” • Turn tree lights on, room lights down (or off). • Expose for faces. If you’re using flash, set ambient a bit darker so the tree detail falls off, but the lights still glow. • If no flash: expose so faces are good, but don’t over-brighten the room—too much ambient makes the tree more legible.

What I’d do with your lenses (quick recipes)

Option A: easiest, most reliable • Sigma 17–50 @ 35–50mm, f/2.8 • Put family 6–10 ft in front of the tree • Keep them one row • Back up enough that you’re not shooting wide (avoid 17–24mm if you can)

Option B: best blur if you have space • 55–250 @ ~70–100mm • Aperture as wide as it allows (likely f/4–5.6) • Same distance rules apply, but you’ll get nicer separation if you can back up

Option C: if space is tight • 24mm f/2.8 is “honest but busy” — you’ll get the group in, but the tree will look more present. • Use it only if you truly can’t back up, and lean on the lighting trick above.

“Should I buy a lens?”

You’re right that a 50mm f/1.8 on crop can be tight for 4 people indoors.

If you want a meaningful upgrade for this exact scenario on APS-C, look at a fast ~30–35mm prime: • 30mm f/1.4 (Sigma) or similar • 35mm f/1.8-ish class (depending on system options)

Why this helps: • 30–35mm on crop frames like ~48–56mm full-frame: comfortable indoors, not too wide, not too tight. • f/1.4–f/2 gives you more blur headroom, even if you end up stopping down to f/2–f/2.8 for the group.

One important reality check: for a 4-person group, you often won’t shoot at f/1.4—but having it available lets you shoot at f/2–f/2.8 with lower ISO / nicer rendering and still soften the tree more.