Euthanasia at home.

I have wanted to keep my cats in their own home for euthansia, instead of going for a traumatic car ride, and then into the vet. I'd rather hold them as they pass instead of watching the vet insert the needle, and waiting to hold them until they have...

already gone. If there was a humane, reliable way for me to do this final act myself I would do it. I am not proficient with firearms...thinking more of a lethal dose of sedative?

The general feedback on this topic in relation to pets being euthanized at home is to get a vet to do a call out. Not sure entirely where to start but it's worth trying your own vet or an animal hospital / clinic.
Other suggestions include talking to large animal vets as they see to animals on site and so would probably have no problem coming to you.
Hope it helps.

How about phoning your vet for advice on what dose to give your animal of what and if it is allowed? I don't know about the laws regarding it in your country, so maybe that is another one.

Otherwise you could always ask your vet if it is possible for him/her to come over instead of you taking the animal over there.

Your vet can come to your home, you can hold your cat while the assistant holds off the vein and the vet administers the fatal plus, it puts them in a state of being anestized first, then once they are a sleep the organs shut down, very peacful and humane,
Call your vet, doing anything at home could go wrong and be animal cruelty