hi littleladylovleyfox,
Ok, I'm just re-reading your post and it seems a little vague to me as in to what you're asking.
From a tax point of view, I think you'll need to first determine your tax status in regards to the US and the UK. I think you currently will be domiciled to the USA which means for tax purposes you pay into the USA tax system first and foremost. As you are 'resident' in this country, you may need to look into changing that so you become UK domiciled.
I'm sure Lizzit & Guya can give you a little more pointers on this as they know much more than me about the tax systems than I do.
It's best as questions come out to speak to a US/UK tax advisor specialist who will be able to show you the differences, benefits and possible drawbacks of your tax scenario - but seeing as there's literally, thousands of couples/families liek yourselves this shouldn't be much of an issue to discuss. Once you add in foriegn investments, income, homes, sales/disposal of assets etc etc things do become very complex - however I do know for a fact many many individuals who have this scenario use software like TurboTax (in the US) and Taxcalc (UK) to accurately calculate their tax liability and make use of an accountant maybe once a year to double check everything.
A mortgage - well, plenty of advice on what to look for - nip into WHSmiths, and I'm sure they still do a magazine called 'What Mortgage' or 'Which Mortgage' - so that would be a good start and then look online for further info.
I'm not sure what you mean by 'a way around it' - I think joint mortgages here have the salary multiplier of 2.75 of joint salary, I don't think you can say oh well I'll just have my salary multiplied by 1 and my partner has 1.75 of it please - I don't think it works that way. Recently, with the amount of different mortgages available you might find that to resolve that element you'd like, maybe your other half goes for one of the 4 or 5 times salary multiplier mortgages - however, I'dadvise caution on those as it encourages people to take on more debt than normal which means higher risk. Even more so now with the global credit crunch taking effect - for instance, 100% mortgages are now much less available.
As ever, start doing some research and weigh up what suits you and your requirments from all the options, it is a minefield of different things out there but stick at it and you should find something suits.
Also, when you say upgrade your home, do you mean to sell your current place and move into another property? or do you mean you want to stay at your current place and extend and refurbish it?
Hoep this helps a bit!
cheers, DtM! West London & Slough UK!