Q:

What are these two intruders into Rudbeckia seedlings home?

I started black-eyed Susan (Rudbeckia hirta) seeds in a tray - you can recognize her seedlings by hairy true leaves. However, I noticed there is another type of seedlings of unknown origin, that looks differently:

Apart from having different leaves, they are also legier. From different angle:

There is another one that appears to be of the same kind in another cell:

From different angle:

They are the only two of such kind in my 44-cell tray.
What are they, and what to do with them?

A:

Looks like a type of lettuce... Lactuca sativa
Below is a photo of our pot of “Summer Harvest” seedlings. 

I not certain what variety you have. 
My recommendation is to carefully remove these seedlings from your tray of Rudbeckia and place them in a small pot of their own to grow on. Once you’ve transplanted them, don’t forget to give them a drink of water with a half strength seaweed extract to help alleviate transplant shock.
Once the lettuce seedlings are larger, you can plant them in the garden or into a larger pot. 
If you need advice on how to remove seedlings from the tray, let me know and I’ll update my answer.

