Shop for a mortgage loan to get the best rate. Using your mother's lender may or may not help you save money.
Using the same agent will not save you any money. Even using the same mortgage company won't help. You might save lots of money by working with a great negotiatior who is YOUR buyer agent. That's their job . It's not t he listing agent's job to save you money but to get the most money possible for the seller.
Work with the lender that gives you the best deal, and the one you feel most comfortable with. Know that since this is a non-arms length transaction, there will be a lot of scrutiny in the underwriting review process.
As for hiring a real estate agent, you don't really need to hire agents for this transaction, although doing so won't hurt. Since you are the buyer, you don't need to be represented by an agent in dealing with your mother as the seller (unless you feel you need it). If you know the purchase process, and have a valid purchase agreement, your purchase should not have a problem.
I'm always available for your questions.
As long as you feel comfortable & confident that they are the best agent to represent you. Yes, you may use the same Lender and Realtor to assist you in the purchase of your mothers home. With regards to any savings with the Lender, you would have to confirm that with them directly. It certainly would not hurt to ask the question. I would also recommend that you speak with a couple more Lenders to secure additional quotes to make sure you receive the best possible deal. Best wishes!