'Should we feel bad?'
What an unusual question. I mean, either you do feel bad or you don't... I don't believe there is any 'should' involved in feelings.
Do you believe they ought to be grateful for the improvements you've made on their house?
The problem here arises from two sets of people with genuine concerns not taking the time up front to establish the contract, and instead relying on assumption, unspoken conditions and expectations (expectations a friend calls 'future planned disappointments)... that you all naturally and automatically agree upon and understand all the same things. Notice how well that works in the average marriage, and then add another couple. Yeah... see - this is just not surprising.
Had you drawn up a contract (about ownership, property rights, improvements, maintenance and anything else any tenant agreement would probably include) you wouldn't be here now. And, now you are here.
I would recommend getting a mediator before your relationship falls apart completely. The mediator should work with each of you separately to find out what all the 'unspoken but definite' terms of the original contract were assumed to be, and then present the group with the results. You will all be shocked to find out how very, very different your opinions on the matter have developed. If you can barely afford it, I would strongly suggest that you pay for the mediator entirely.
By the way, the 15 miles to school is a personal choice that has absolutely nothing to do with this issue. You will find it easier to deal with all issues if you focus on the heart of it rather than extraneous choices you made for your own reasons...