the first is a Cirsium, maybe Cirsium rivulare
the second Lysimachia atropurpure
3 is Nectaroscordum silicium
I don't know 'White Swan' but it's euphorbia and I think it is flowering.
the leaves are similar but the stems and manner of growth are different. Can we have a look underneath?
I think they're ornithogalum, Star of Bethlehem. Pretty flowers, later than other similar bulbs and very tatty before flowering is over. Quick to multiply as well, maybe a bit too quick
agree with borderline. Dianthus. I had some that looked like that, from a packet of seed called Dianthus 'Loveliness'
borage seeds a lot but easily removed. I wouldn't call it a problem plant
I should think it's at its most nutritious when the leaves are fully formed but before it puts effort into making flowers, you can harvest the lot several times a year like that. Need to keep one for the bees though
If they're first year seedlings I'd pot them up til they're a bit bigger. You're right, sand won't keep them going for long. If you have good soil (not heavy clay) you could put them in the garden but it would be easy for them to be swamped in summer
Did they stay at that height and green all winter? or as a bit of green at the base?
Most of mine do that, it's normal, especially for big ones