Fuel allowance is paid for 26 weeks so add 43 pm to income. Average support to your daughter the same way, if for example you have to give her 50 a week for 10 weeks of summer then add 42 to monthly costs. Make sure you put in something for house maintenance as well, an average of 40pm is usually acceptable. Also the section for gift, birthdays etc, (can't remember exactly what the heading is) put in something there, everyone has to buy kids birthday presents etc, allow a small amount but allow something, the category is there as it is expected to be used.
Average everything out and make them into monthly figures, all these details will be input by your lender into whatever computer programme they are using to determine how much you can afford to pay. Doesn't always work though!
Check the totals yourself when it is done before you submit it, if you are showing a minus in monthly income excluding the mortgage payment then it gets awkward as they cannot offer any kind of solution if your figures show you can't afford anything. Ideally if you want interest only or reduced payments then your monthly surplus should indicate that you can pay that amount, not saying to be untruthful with the figures, just be realistic. No point agreeing to paying something you cannot maintain, better to agree to a realistic figure and stick to it.