The best plane for your father in law is an Ultra Stick. It's available in 40, 60, 120 size. The 120 size is big and can be flown with a Saito 100 or 125. It lands super easy, isn't affected by wind much and is big enough to see well. The 60 size would be good also and could go with a Saito 100 or 82. Either is the perfect plane. If he can't fly one of these, he just won't ever get it.
Thanks
Bud