Your vet is the person to advise on this. There are other conditions which may show similar symptoms but require different treatment.
I have used Panacur on an older, disabled / frail rabbit with classic signs of EC. He was already on metacam - which is also needed for the treatment of EC as it reduces the damage done by the parasite. Panacur just works on reducing the parasite load - the symptoms are neurological damage caused by the parasite, and an anti-inflammatory (eg Metacam) reduces the symptoms.
If there is a reasonable diagnosis or likelihood of EC, it is sensible to treat all rabbits in contact / share the same space at the same time and for the full 28 days. The spores are shed in urine, so there is always the possibility of continually becoming infected, shedding and reinfecting other rabbits. In order to break the cycle, treat all rabbits at the same time and deep clean their whole environment on days 21 and 28 of the treatment cycle.
If you are treating multiple rabbits, it can work out cheaper to get a bottle of 10% liquid panacur sold for cats & dogs (vs the syringe paste marketed for rabbits). It can be bought without a prescription from various sites online (eg VetUK), and some pet stores. As I understand it, Panacur is a relatively 'safe' medication - but check with your vet for your circumstances. A blood test can check for kidney / liver function (to check that they can tolerate treatment) and for an EC titre to see if there may be an active infection.
Metacam is a prescription-only medication.