Weddingbee boards

My Finace and I  live in Canada near my immediate family, but he is English and has alot of family and friends there, my Mother is also English with a large family in the same area. 

My Fiance and I are planning a small wedding at my parents cabin on one of the gulf islands on the west coast of Canada.  The idea is that our immediate family a few of close friends from Canada  will join us.  Our immediate families are large so thats about 35 people.

We plan to follow this a month later with an informal party at a pub in the UK and invite all our English family and friends to celebrate with us there.

both of us want something very simple and don't have much money to spend (we will be paying for everything ourselves).

How should we go about inviting people

1. What wording should i use to make it clear on the invitation that it will be small and rustic so that people are prepared for scale of the event and to dress apropriately -it is at a  waterfront cabin.

2.  Should I be sending wedding invitations to my family in the UK (Aunts and Uncles) it is very unlikely that they will fly out for our wedding as they haven't for my siblings but it is nice/ apropriate that they be invited...?

Also I will be haveing my best friends at the wedding should we invite my Fiance's best friends from the UK some are already assuming that they are invited...we don't want to offend anyone we have been to their weddings but it is a long expensive flight to come to something EXTREMELY low key and it may be a somewhat awkward mix

we don't want people feeling like we will be upset if they dont fly out to our wedding because we don't really want people too :-/ there are some people who it would be extremely rude not to invite.  But we are really trying to keep numbers to a minimum.

sorry this is long..... I am finding it all very stressful!  my soon to be inlaws don't seem to get how low key our wedding is going to be (they keep asking about marquee's etc) no matter how we try to explain it to them!