You can change the pedals for sure. They’re standard threads. There are also cages that have clips on the bottom to work with peloton pedals.
For the seat I think you should be able to change it. Hope the rails are the same width for attachments. The link you have is to a seat cover which will slip off the standard saddle. There are links in the listing to comparable saddles.
Not sure if it would be useful in your brothers case but I picture having those home dip bars by the bike to help with on/off and possibly to grab in a severe loss of balance
Good luck!