I think I saw an ebay lot for these. I remember being interested at the ballerina tutu (with a good purple and the tutus are harder to find and sell for almost as much as a pony), and sunspots hair still with pinkness (this is an advantage as it often faded to white) and sun gliders wings are still in good condition. The purple curls on Twinkle Dancer ballerina pony are good and Tossles & Romper happy tails still have a light curl. At the time it was listed I did a check of all the ponies for any of the clips, barrettes etc as they are useful to buy/sell even by themselves. I wish you luck for the sale. I would have started a little lower given the condition they are in but it is always good to try first and then if they do not sell see if you want to go lower and let the market decide on later runs.
If the auction does not go through on the first round a light wash of the body could help to lift most initial grime e.g. dish soap/water & soft toothbrush or isopropyl & cotton tips; being careful to not wet the hair or get liquid inside by tail hole, neck or head holes (a restorer could do more thorough cleaning and reduce any internal rust chance), and avoiding pressing/scratching/rubbing symbols, eyes & cheeks (especially the magic message cuddles teddy bear symbol). Initially the symbols on yours look good and avoiding them, eyes and cheeks is fine at first clean run. It could probably help as some sellers who might be nervous on the layer of grime & dark marks. They don't look like marker or deep ink so they should be easier to lift. Just the usual grime that a light wash could lift some and a buyer could try more thorough clean and restoration to remove the rest including some colour marks. The pink marks on Baby Stockings neck look like just from the hair and should be able to come off if there was a restorer as buyer who could use stronger techniques.
There is a highly trusted Ebay seller who is prolific at selling ponies with some love needed but they do an initial clean run, check for marks or hair cuts and then they start auction prices quite low for most with small marks/minor flaws e.g. 6-10, or for the sparkle 12-18 with minor flaws, but the ponies can sell for much higher in auctions. Twinkle Dancer (I definitely would price around 25) and sparkle Sunspot are likely to be the gems, wing Sun Glider with a light clean would be good as well (Sun Glider strangely sells closer to the other summer wing ponies prices rather than the other windy wing ponies; you probably would not need to clean wings, best to avoid/reduce wing breakage on first run). Once cleaned a little the brush and grows Pretty Vision and Twisty Tail should do much better in buyers calcs; as they are it is hard to tell how receptive most buyers will be and deep body cleaning can take a while. For buyers an initial cleaning pass is appreciated so they can see more clearly any harder to remove marks/ink/discolouration/mould/stains/spots etc.