No solution will be ideal, but I'll bet it can be done! With the water toys on the tug roof you may be over the weight
limit to add the bikes up there. Maybe put one bike there, and the other on a rear trailer mounted rack. Putting the bike on the front of the trailer above propane
has been done, but may interfere with the kayak overhang. If you use a rear of trailer mount you will have to pay close attention to keeping shiftable loads way up front for balance. I use a rear mounted platform on the back of our 16' Scamp
to carry a campfire pit, wood, and accessory tub which all together weigh in around 70 pounds. It tows fine if I put heavy stuff in the front bath and area just inside the door. Two bikes would be in the same weight area. I did relocate the Scamp's axle
back 1" from stock which helped in my case.
Having bikes at a campsite is necessity.