Pressure washing is the first step. It might remove some loose paint but don't try to force the removal. Pressure washing can easily damage wood. Scraping is your best bet to remove the loose paint. To make the rough edges smooth after scraping will require sanding. This is especially difficult with redwood.
You could try using a random orbital sander with 60-80 grit discs. Be careful, it will be easy to remove wood and not do much to the rough edges. If this is the case, simply do a good job scraping and leave the rough edges.
O.K., the primer. A stain blocking oil base primer is needed. Redwood has tannins and this will bleed through the acrylic primer, even when they state 'Stain Blocking'. The great thing about primer is you can use any kind of paint over it. For a good result and better experience painting use a good 100% acrylic paint. Using a stain now won't work. You would have to strip the entire house, not economically feasible.
I think that peeling will always be an issue with your house. The lack of primer, when needed, and proper prep has doomed future paint jobs. Do the best you can or hire a good painter to do the work. Not cutting corners now is the only way to get more than a couple years out of the paint job.