Yes, it is certainly possible to combine mortgages into one monthly payment. If the mortgages were taken out simultaneously, it would be called a "rate and term refinance". If they were taken out at different times, it would be done as a "cash out" refinance. Regardless of what it's called, the qualification rules and process are much the same for each.
1. Apply for a loan with your current lender. They will usually waive some costs and fees in order to keep you as a customer. This is the cheapest option in most cases; you should ask for information on refinancing and tell your lender that you want to consolidate your mortgages into one loan.
2. Fill out the mortgage application, which is called a URLA (Uniform Residential Loan Application). Don't forget to add your full name, birth date, and the last two years of your income, residence and employment history. You should also provide your last two months' pay stubs and bank statements, as well as copies of your W2, tax returns and assorted other documents.
3. Ask for a "good faith estimate" and a copy of the Truth in Lending statement. The estimate will list the costs associated with the loan, as well as the term and interest rate associated with the loan. The Truth in Lending will list the annual percentage rate. The APR is the total cost of the mortgage, including the interest rate and fees.
Allow time for your application to be processed, and then it's closing time. Sign all the paperwork, and the closing agent pays off the two old debts and rolls that amount into your new mortgage. Keep in mind that the best interest rates are given to those with good credit scores. It's a good idea to review your credit report before you apply to combine your mortgages, and if you find errors, get them removed immediately.