Why do you care what they think? If you're adult enough to get married then you need to be adult enough to not need Mommy and Daddy's approval or have them dictate your life.
If you and your fiance have decided to move into the home that he already owns, then that's between you and him. Simply say to your parents, "Thanks for your concern but we've got it handled" and then change topics or end the conversation. If they keep bringing it up, curtly say, "This is not up for discussion. I told you, we have it handled. Do not bring this up with me again" and then walk away/hang up the phone.
Your parents will always have their own opinions about YOUR marriage and YOUR life, whether you ask for their advice or not. You are not obligated to take their advice. Learn how to nip it in the bud NOW or else you will have a miserable marriage and an unhappy husband who doesn't want his in-laws constantly butting in and his doormat wife always changing the marriage plans because Mommy and Daddy have a different opinion.