Labrador Rescue (lots in various areas), Black Retriever Cross Rescue (Jemima is the contact, they take full Labs too), your local no-kill rescue... any of these and many others before you consider privately rehoming.
Why do I say this? Well, can you:
Check the new home without embarrassment or favour?
Do follow up checks after you've rehomed privately to ensure the dogs are ok?
Assess that home for suitability drawing on great experience?
Offer lifetime support to the new owner?
Take the dogs back if it doesn't work out with the new owner?
Vaccinate and medicate prior to rehoming? (I know that the answer to this is no of course!).
A good rescue CAN and WILL offer these things and more. Offering your dogs to strangers over the net is potentially putting them at great risk unless you can match what a rescue would do. Please remember too that not all rescues use kennels, many offer a home from home with foster carers. Equally there are many rescues who will take a dog/s if in serious need despite the fact that they are many miles from you. Some have this as their policy, some will only usually do this when they get to hear of dogs in need via rescue contacts like myself, so if you can't offer all of the above I would really strongly advise that you approach a rescue rather than rehome privately and if you have no joy with those you contact please put a shout out on here for me and I'll give you my email address, speak with you there and give my phone number and references and try to help you in communicating with appropriate rescues on your behalf.
Am using my DCs laptop as mine is playing up but somewhere on mine I have the contact details of Ben at Labrador Rescue too, so if you need them or any of the help I've offered/advice, please post here with my name in the title so it dawns on me to look at it and I'll do my best.
Locally to me there's a rescue who have and currently does walk and help with meds for dogs like yours as we know that they, especially older dogs in a loving home, are best staying there if at all possible. I know that this rescue is one in a million but if I can find similar help and you would find that do-able, I'll have a go... just ask.