Marrying without her father’s knowledge

I am looking at a lengthy engagement period
before my fiance and I am able to financially marry and live together. We would both like
to have a nikkah during our engagement so that we are not sinning when we are intimate
with each other. However, both of our parents are against this and want us to wait until
our marriage reception which is in a year or so. Is it allowed for us to get a nikkah in
secret? My second question is, is it ok for us to repeat the nikkah ceremony again during
our reception (since our parents won’t know of our first nikkah)? Is a double nikkah
permissible to the same person? Your help is much appreciated.