There could be several issues:

1. Stress from the trip and not accustomed to you or the new surroundings.

2. Swans get rather perturbed about being brought indoors and will pout---no eating, standing, etc., until you are completely out of sight. Then, they will find the food and eat it as long as you are not around.

3. There is an injury. Without having a full exam, we cannot surmise if there is a problem. However, looking at the photo, it appears that the swan's leg appears to be splayed outward which could prevent any weight transfer for standing. You might try to place its legs under the swan in a normal position to see if this helps. Do Not force its legs, just place them in a natural position under the swan and walk away. See if he tries to stand.

The best thing for the swans is to get them in a water feature so they can swim and exercise their legs. Just ensure that the swans are placed in a safe area free frim predators and which they cannot walk away. The substrate must be free from an abrasive or slippery surface. The water feature should have a zero entrance with no steep banks, but an entrance they can easily float in and out of the water without having to climb or strain its legs. We hope this information is of benefit to you. The Regal Swan