Hi Gemma,
I'd reccomend getting a copy of your credit record to find out what it says, and you can see what the lenders will see also.
Regarding the remortgage, there are 85% deals out there (90%), and obviously the deals aren't as good as the 75% or 60% mortgages.
Looking at your credit record will help determine when defaults etc will clear your record.
Do you know what your SVR on the mortgage will be when the current deal finishes?
You do not need to remortgage, you are already in a deal, but the special deal (fixed) ends and then you go on the SVR so you are not at a complete loss, and also your SVR should be a lot less than 7.9%
Whether you decide to buy the other part of your house, I would recommend paying your other debt first.
Having 2000 rather than paying off the debts may be better to reduce your mortgage.
Speak to an IFA / broker about what they can find you and the benefits of having the 2000 vs paying off the debts.
Good Luck with it
Sparky.