Your father's bike collection is stellar! Many of us would be proud to own just one of those bikes. I agree with the sentiment of trying to restore with period parts any bikes you plan to keep. Fortunately for you Ebay UK is a good source for most parts you might need for those bikes.
I agree with the approach suggested by
SurferRosa . Start with one bike. You'll learn a great deal as you work your way through that one bike. Don't let the enormity of the whole endeavor deter you. The folks here are very knowledgeable and very helpful. When you aren't sure how to proceed post a photo or two of your project and you will get lots of help.
If you and your father are planning on selling any of the bikes don't put any more effort or expense into that bike than finding the correct parts in the collection to go with it. It is difficult, especially for someone not familiar with the nuances of vintage bikes, to recoup any money you put into them.
Brent