Most recommendations are to just cull the weakest. Being tomatoes, you could always root them if you wanted- to avoid damaging the roost system of the keeper, I would snip the weakest at the base, then root them (there are probably many discussions on how to root cuttings, and a quick google search has many tutorials).

Another option is to do an experiment- multisown tomatoes. It could be a fascinating result.

Agree that had they been planted further apart or separated much earlier you'd now have 3 seedlings but too late now as all their roots are totally entangled. Sacrifice the one with no true leaves, snip off the other one at the soil level and root it separately.

Dave

Or just plant them all out together. They'll pretty much behave as a single plant with three main stems. I usually thin to doubles, and plant the two together.

What kind of tomato are they?

They are Bonnys Best tomatoes. I do have 11 seedlings but these are some of the bigger ones.

I separate tomato seedlings all the time, as floraluk suggests. Very rarely lose one. Out of about 60 tomato seedlings I had this year, lost about 3. Go slowly and if it doesn’t look like it’s going to work, have scissors handy and just snip the weaker off at the stem. Use a good balanced liquid fertilizer when potting out and they’ll form roots just fine.