If they are dyslexic or show “significant difficulties with developing language and literacy skills”, they should have reasonable adjustments in place (remember you do not need a diagnosis to have a condition). As long as you state what school will be doing to meet their needs it is probably OK.
I would focus on non-decodable words and teach strategies for others. Make it as multisensory as possible – speak it, hear it, taste it (?) touch it, feel it. Write in pen, pencil, sand, foam, paint on computers (not foam or paint!) sing it, dance it, shout it. Whatever it takes.
Don’t worry if they can’t write it yet if they can read it.
Put the difficult words on the back of the toilet doors (no point on letting them waste “poo time”)
Celebrate success….we don’t have failures so just celebrate getting them right at another time.