Here's a link that may help you estimate the potential lumber quantity:
You 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.