In reply to Lbet:
Hi
Agreed that the Llanberis path is the way most novice walkers go.
It does has a very steep first 10 -15 minutes up a lane before getting on the path proper. This can knock the wind out of a lot of people right at the beginning. After that the path is a steady rise to Halfway house before climbing steeply again up to and past Clogwyn Station. It levels out again before a short pull to the summit.
If you allow somewhere in the window of 6 - 8 hours you could have a steady walk with breaks and take in the views.
If you have done Cader Idris then Snowdon should be within your compass. You need to have a think if the other couple you are taking would be ok with a 6 - 8 hour mountain day.
If not, there are plenty of shorter walks in Snowdonia. Like around Llyn Idwal for example or a smaller peak such as Moel Siabod, where on a clear day you would have an awesome view of Snowdon.
Personally if I was to introduce someone to walking in Snowdonia I would choose one of those two.
If you go with the Llanberis path there are sizeable car parks but the advice would be to arrive early, around 9am. Also bearing in mind you may have a long day.
Hope that helps.