I have a an engineering firm and I would like to use it for buying rental property, can I do that or I need to open a specific LLC for real estate investment ? also what kind of insurance I should need for the real estate involvement LLC ?
You should not use the same LLC. Real estate is taxed completely different than an active business, especially if the real estate you are buying is rental properties. Also, starting an LLC for real estate before you've really begun tends to be an issue of putting the cart before the horse. And there are a lot of disadvantages to going the LLC route.