Here's a link that may help you estimate the potential lumber quantity:
formatting link
can calculate for each log or the whole group. Example: 40 logs, each about 15" in diameter and each 8' long will total about 2800 bd ft. Depending on the cutting method, this volume can be a bit more or less by 5% to 10%.
If you decide to cut the trees yourself, for future milling, don't cut them shorter than 4'. Most mills, including portable mills, can't handle anything shorter than 4'. The clamps on the mills, that hold the log while sawing, are spaced 4' apart.
If you decide to keep the lumber yourself, and for maximum bd ft, have the miller scab two adjoining sides, place log on a flat side, then saw the remaining log using the through-and-through method. With this method, about 1/3 of your lumber will be quarter sawn, and that 1/3 will be right through the middle of the heartwood. The outer cut boards will be more apt to warp, twist, check, etc, but if you dry the lumber in a way to prevent or reduce most warping, etc., then you'll usually have some relatively nice patterned lumber for some particular project that highlights the grain. The through-and-through method is the fastest for the miller to perform, and if he is working by the hour, then the cost will be the least. And by initially scabbing 2 adjoining sides of the log, before milling, one edge of your finish boards will be a straight edge, hence you can dress the remaining edge (board width) as you want more conveniently on the table saw.
Does your house construction plans include beams or support posts? I can see some nice beams and posts in those trees you have.
If any of your trees have the potential to have been in an area of people or along an old fence line, there may be the potential for the lower trunk to have nails, fencing or other metal debris imbedded in the log. Millers don't like to hit metal with their saws. But your trees sound like they may be in a relatively rural area, and not be prone to having metal imbedded in them. It's just a consideration millers have about milling privately owned logs.
Sonny