Jordine,
You've got your work cut out here, but this is how I would approach this,
1st can you remove all the plants weeds etc growing through the Gazebo?
2nd try to remove with a stiff brush all sh*t that is on the deck floor. You may well find some rotted boards when they get this bad. If they are in good condition then give it a pressure wash water only, see what stain (Ronseal) is left.
3rd So let's say there is some stain left then yes Prep-deck go in at 3:1 first and see what this does.
If it looks like you have removed the Ronseal, then follow-up with the Netrol, if not and this will be in the grooves mostly, re-apply the Prep-Deck but up it to 2:1 and allow a bit longer dwell time, bot do all the floor don't spot clean.
On the cladding & Gazebo remember to work from the bottom upwards when applying any chemical to avoid runs. Really pre-wet everything as this wood is going to be so dry (natural oil) and will suck up whatever you are putting on it.
4th Once you have the wood clean & stain free, you can defiantly sand the Gazebo and the floor, hopefully the grooves will be clear of Ronseal. Proflle/detail sander for the groves, random orbital for the rest of the wood. Remove raised grain and any dead fibres as there will be some when wood gets this neglected and after the above cleaning process.
Once this is all done, then re-oil.
It look's daunting but is doable, you just need to charge accordingly as there is a lot of work to do to get the right result. But if the decking boards have rotted then they will have to be replaced, no point in messing around with rotted boards.
Re the Roble Wood, it's a very dense hardwood (Bolivian) so a lot like Ipe. It should look a nice warm honey colour, you can clean it like Teak, a photo would be helpful.
I have some photos of Roble we have done somewhere, I'll try to put them up later.
Good Luck
