One further thing to add, you can move players between Sevilla Athletico and Sevilla 'C'/ U19, whilst also moving players from the reserve team to Atletico. This also affects the wage bill so just shift some of the dead wood from the team to 'C' and you will have cleared some of the problem.
Sevilla Atletico is the reserve team for Sevilla, so whilst you may have the power to buy in players, I presume that the ability to get rid of them depends on the parent club. It appears to be the same with Barce 'B' and Castilla (the two more well known reserve teams).