yes, agree, see an independant financial advisor - they will have no bias in the game whereas doing a DIY will mean that you are prioritising HIS views of what is the best, which may not necesarily be the best for you.
In regards the rest, well I agree with others that you should be paying proportionally into a joint account that covers all family outgoings, with an agreed amount maybe going into a holiday / renovation fund, and an amount from each of your excess going to a personal pension if needed. By all means use the credit card to top up, but if you are regularly needing to do this, then ideally you are going to need to pay a little more into the bills account each month.
This joint bill account also includes your kids outgoings too. Im sure they will have applied for student finance - so what did that come up with as the parental contribution? It likely would have been a lower rate due to being a home student and not living in halls, so their travel, food and expenses should be budgeted for out of that 'contribution' amount - if they need extra then they could look at part time work like other students.
I feel that you are only accused of being spendy because you have less income and have effectively been covering three people - its an easy trap to fall into, but think - if you had applied for child maintanance for the kids, how much would it be viewed that he should have paid each month, and perhaps hasnt, because youve been covering kid expenses.
You have a good combined income. Financially its simple to see how much he would be obliged to fork out, either by child maintanace or parental contributions - these figures are readily available online - how less 'spendy' if youd had even half that amount to contribute and not had to hide expenses for the children. They should be having driving lessons on that income, giving them independance to get to Uni, to look for jobs. To have £1700 spare from his wages, after squirrelling away some in a saving account - he can easily afford that. And as for a spreadsheet of what your kids will 'owe' - Jesus, thats disgusting.