Hello António,
unusually well-preserved corals!
My recomendation is not to use any acid on them. Acid preparation is suitable for silicified corals only, and yours rather look calcified. The matrix looks like marl or soft limestone, am I right? You might then use a dishwashing detergent: Put the corals into concentrated detergent and wait approx. 24-48 hours. The detergent might be able to soften marly sediment so you can just brush it off under running water. Don't forget to put the coral into clean water for another 24-48 hours to get rid of remains of the detergent that might have dissipated into the rock. If the method fails (means, has no effect at all - you actually cannot damage those fossils with dishwashing detergent), you should consider mechanical preparation.
The sea urchin looks like a Clypeaster and rather seems to be of Tertiary than Jurassic age to me.
Best Regards,
Rainer