Good luck. Walnut is bringing a good price right now. typically trees growing in a yard arent that great, but cut them as long as you can to try for a vaneer log. Then cut them farther up until the log is around 14 inches in diameter on the small end. If the logs are cut and laid out I'd get at least 2 bids on them. You should be looking at 8 logs off those 4 trees. If your local saw mill is trustworthy then just deliver them have have their buyer grade them (to make it easy).

You wont know until the trees are cut what the quality is. But, around here it isnt crazy to get several thousand per tree.