So, let me just clarify your situation:
About a month or so ago, you found Pearl in your garden, took her in and have not managed to find her previous owner.
Then after a few more weeks you bought Sunshine and put her in Pearl's cage with a divider between them.
Why did you decide to buy Sunshine?
Did you realise that quarantine guidelines should have been followed (meaning separate cages, in separate rooms for a number of weeks)?
Did you read the sticky advising how to gradually introduce new birds to each other?
Yes it is more difficult to tame two birds than one but a month or so is not a long time in this process.
To say you're doing an awful job would be very harsh but now that you have found this wonderful site, you really need to sit down and read through the list of stickies, they'll likely point out where you've gone wrong and how to back track and do it right.
There is so much useful information in there:
List of Stickies
You'll probably find these the most helpful to start with:
Yes, Your Bird IS Scared!
Introducing Two Budgies
Quarantine IS Necessary!
- though this is too late now.
Essentials to a Great Cage
Suggestions To Help You Bond With A New Budgie
Some minor squabbling is normal between budgies. If your budgies squabble too much to be housed together or if the divider doesn't allow the birds enough space, then you'll need to house the birds in separate cages. If you haven't got another cage and can't afford to buy one, then you'll need to rehome one of the birds (or return to store if that's possible).
Letting them out in your bedroom - it's good that you've considered the windows and mirrors, other than that, I'd just try to minimise clutter as much as possible and try to position things so that they can't easier get stuck behind large pieces of furniture.
Place their play gym beside their cage door with small treats attached (millet, toy they like, romaine lettuce) so that they're encourage to explore it. Once they're used to popping out and confidently perching there, you can gradually (over a few days) move it to another place in the room.
I wouldn't consider swapping Sunshine for a male, it may be the case that Pearl is used to living as a single bird and wouldn't be any more accepting of a male bird's company. Also, if you can't afford another cage, you need to think practically and consider that fact that two birds also means two sets of potential vets bills.