Motorcycle of 2 riders once open and once throttled “simultaneously” driving

Hello guys, I have a question that I haven’t found in a forum yet. My father (Leader’s license A) bought a Ducati Monster 797 which he wants to drive in April. I currently have the A1, but can do the A2 in the summer. My dad had offered that I should also ride his motorcycle (can’t afford myself a bigger motorcycle). I would have to drive the motorcycle then throttled and my dad would naturally want to drive open. It’s a problem every time someone else drives in and out of the throttle (it doesn’t happen so often). Actually, you shouldn’t get any problems with the insurance. I would insure them openly (because of A1 SF discount, my dad is “new entrant” after many years). We see the only problem with the vehicle papers, because there is 48 HP there and my dad would drive open (but there he could also pretend stupid and usually get away without or with a small fine). What do you think of this? Make sense? Are there any problems that we have not considered?