I'm very sorry for your loss and that this has happened to you and your rabbits. Unfortunately this sounds like it could be calcivirus (RHDV), particularly if your rabbits weren't vaccinated for it. The bird would be the likely carrier of the virus through contact with an affected rabbit in the wild, or through biting insects that carry the virus. Though it is possible it's not from the bird and this is just a coincidence, or there's another cause, especially if all your rabbits were vaccinated for both RHDV strains. Though I'm not sure what it might be if they weren't showing any specific symptoms.
https://wabbitwiki.com/wiki/Rabbit_hemorrhagic_disease
https://kb.rspca.org.au/knowledge-b...t-my-rabbit-from-rabbit-haemorrhagic-disease/
For your remaining rabbit, you'll need to phone a rabbit vet for advice, but
do not go to any vets office, or at least not without first informing them of your rabbits deaths and the possibility of you and your remaining rabbit possibly being a vector of RHDV contamination from the bird, and them deciding if you would be allowed to come to the office or not.
https://wabbitwiki.com/wiki/Choosing_a_rabbit_veterinarian
https://rabbitvet.net/AustralianRabbitVets.htm
https://wabbitwiki.com/wiki/Category:Australia
If RHDV is the cause, there's unfortunately no cure, with it having a high mortality rate. There is a very slight chance your remaining rabbit could survive, but just know this is highly unusual for this to happen. So be prepared for that. To help your rabbit, at a minimum you would need to provide supportive care of syringe feeds if your rabbit has stopped eating adequately. Your vet can provide recommendations for the proper supportive care needed, and possibly any supportive medications.
https://wabbitwiki.com/wiki/Medicating_your_rabbit
Be aware that if RHDV is the cause of death, that the virus is highly contagious and continues to be so for months. This means that your home and you can be vectors of the potential to transfer and spread the virus outside your home, particularly if the bird is the carrier and you continue caring for it. This would mean that it could affect any rabbit you come in contact with, anywhere you go that a rabbit may have contact with, and your home as well will continue to be potentially unsafe for any unvaccinated rabbit, or possibly any rabbit. Proper disinfection and biosecurity measures can help minimize this potential transfer of the virus outside your home. There's some info on this in the above link on RHDV. You can also ask your vet for proper disinfecting and biosecurity advice.
