Hi and welcome,
Unfortunately the types of issues you've been experiencing are not unexpected for someone in the 65+ age range, so without any MS consistent/sugggestive MRI, LP, VEP, dx Optic Nuritis etc etc evidence to get a nurological condition like MS on the list of most likely causes, conditions more common to your age group like DDD, osteo, peripheral neuropathy, RA, thyroiditis etc etc would still have a higher possibility....
outside the box but have you considered a 3 wheel recumbent bike, its the type of bike that provides you balance stabily and is easier to peddle, but you can get them with an assistance motor too. Dogs can toddle behind or along side and if you put a basket on the back, when their little legs have had enough they can ride home happily with tongues and tails a wagging :D
Hope that sparks some ideas......JJ