A lot of people here in Holland use these special bikes with a box on the front.the bikes are long with a big box which rests low close to the ground,easily big enough for your 2 dogs.The dutch transport kids,dogs,shopping in them.Also,I believe swimming is supposed to be good for arthritic dogs.If you have lake or beach near by you could cycle there with your dogs in the box and put the one with arthritus straight into the water