The house has always shared the attached neighbour's septic tank. For
various reasons I am looking at terminating that arrangement and
installing a new system for waste water and sewage. There are no public
sewers. I am in need of some initial guidance, not really knowing where
to start.

I have heard I think that septic tanks are old hat and that there are
better ways to deal with sewage but I don't know what they are. Is this so?

The land attached to the house is all uphill slightly and access for
large vehicles (bigger than a big van) could be a problem. does that
rule the idea out?

Connecting to the house will involve going through or under concrete
foundations (existing connection to next door is under the rear
extension). Does that rule the idea out?

Power has never been reliable during winter storms. could be a problem.

Who would design and specify a system? a builder?, an architect?, don't
want a salesman, an engineer? Somebody else?

Tim W