Very healthy looking! Looks like a bit of sunburn but that will not hurt at this point.
Remove the string you have tied to the stick.
They do like a bit more room...2-3 ft apart, 4 is best. And a much stronger stake or cage.
They may easily grow 6-8 ft. Driving in a stronger stake will damage the root system now.
Might try a teepee system by giving support from further out from the roots. Or a circling wire cage out of cattle fencing or similar to your region. (something in a roll that is strong and easily cut with wire cutters)
Use something more flexible to tie them to your stakes. A cage will be a support itself.

Another option would to just let them lay down gently and sprawl out right on the mulch if they have the room.
They look low to the ground enough to accept that it seems...

Thanks! So you don't recommend cutting the stems or pruning stuff?

I didn't research tomatoes before putting the stake through! and honestly, I think I planted them too close together (I also didn't think they would survive... they are about 1ft+ apart.)
I've actually built a greenhouse structure around the tomatoes, how about supporting them with strings (attach the main stems to a string and to the structure above)?
What would happen if I drove a stake through the roots?

The Teepee system sounds feasible. While the last option sounds tempting, I have got ground space restrictions, since I am growing in a raised bed.

Looks like what is called "fused stems" in the pic. Usually from multiple seeds that are planted close together. The string in the pic really should be cut.

Whether you remove 1 or 2 of the stems by cutting above the fused point is up to you but as long as you can support the plant well as it grows I'd just leave it as is.

Dave

Thanks.