My dad who is approaching 60 is doing F1 alongside me and is struggling with the deck squat. He is progressing very slowly and unsafely. He has sprained his wrist and hit is head fairly hard on separate occasions while trying to do it over the past several weeks. He just keeps losing his balance and/or doesn't get enough momentum. He is normally well except for mild right hand/arm weakness from a previous neck injury. Before this he has exercised very sporadically and is overweight by BMI but was previously sporty in his youth.
Is there another easier exercise that he can do for 12 weeks to build up to the deck squat? Or would it be better to just drop this stream temporarily and retry at a later date when he is stronger generally from the other exercises?