As a former realtor, I agree with Sally's reply. Sellers who use "We buy homes" or "Sell your home for cash" are typically having their home foreclosed on and they typically defaulted on their mortgage loan OR they defaulted on property taxes. Either the seller lost their job, had a medical crisis, etc. Bottom line - if you are up to date with all your payments, do NOT use "Sell your home for cash". These people are cash investors and they want homes for cheap prices, so they can fix it up and make a nice profit when they sell it.
The best way to sell your home quickly is thru a realtor. Contact 3 - 5 local realtors and interview them carefully. Sleep on it - do NOT sign anything during the interview. They will try to have you sign immediately. You are NOT going to do this.
As for your new home (the estate), you need to speak with a lender and have them pull your credit. You need to get their opinion of whether you will be approved for financing or not. Do NOT assume once you sell your home, you can buy your new home. Only if you pay 100% cash and have the money in the bank, then you can afford this new home.