Ordinary shares and preference shares are two entirely different things and have different prices.
Preference shares pay a fixed dividend, although it can be skipped if the company is in touble. It is the first dividend a company will pay - hence the term preference. Their price doesn't normally fluctuate very much.
Ordinary shares pay (after the preference shareholders have been paid) whatever dividend the company can afford - therefore it can fluctuate quite a lot - as can the share price.
I don't really understand your question 2., but I suspect not. The ordinary share value might well have risen to 150p, but the preference share value won't have - it won't vary much from 50p.
What it boils down to is you cannot sell your preference shares at the ordinary share price. You sell them at their own price.