Re: how to introduce indoor cats to the outdoors?
10 years old and have been housecats all that time? First, I would think long/hard about how equiped they are (and are not) to handle the dangers of being outdoors. This means vehicles, domestic pets (cats/dogs) and possibly wildlife, depending on where you are living. Were they my cats, they would remain housecats with limited access to the outdoors, unless I had my house in the middle of a large acreage of land with neighbors and roads a fair distance from the house and secure fencing around the property to prevent unwanted dogs and/or wildlife from encroaching upon the 'home area' which should be their safe zone.
With our cats, I would get the neighbor's two boys to come over on the weekend and we'd do what we called "Kitty Cat Round Up" where I'd open the french doors and let all the cats out into the 1/2 acre backyard. About 5-7 cats at that time. The boys, my husband and I would stand in a rough semi-circle and keep the cats contained so they could explore outside a bit. I had a few 'runners' who would dash off; Reilly, Mister and BooBoo, trying to reach the woodline. One person each was assigned to keep an eye on those runners to go after them and bring them back. We would let them explore for about 5min or so and then we'd clap our hands and herd them back indoors.
I do feel this was beneficial as it allowed them to become familiar with their area and where/how to get back in if they ever did escape.
If you want your cats to become more familiar with being outdoors at your new place, I would let them out with you, one at a time or with two people so each person could be in charge of one cat. Let them explore for longer and longer periods of time, until you felt comfortable with them being outside on their own. They need to know where there home is, where to find their food and water and if you are planning on having them outside the majority of the time, you must provide a safe place from both weather and other animals who could harm them.
Best of luck,