What are my rights if when our grandmother passed she left my brother and myself 2 adjoining properties each with a house?

While no lawyer can predict the outcome of a court case 100% in advance (judges can do strange things sometimes)--never trust any lawyer who says he can--you most likely correct: it probably would be a 50-50 split:
1) At the most basic level, the share you receive when an asset is sold is proportionate to your ownership interest. A 50% owner gets 50% of the proceeds, because as 50% owner, you are legally entitled to half the value.
2) While there are "equitable" (essentially, "fairness based") doctrines that a court could use to modify the above, while your brother has a point about his paying for remodeling--many judges would take that into account and give him more of the proceeds to compensate him for the investment he made which facilitated the sale or contributed to the  value--you also have a point about him having lived there "rent free" for  7 years--judges could also hold that he has already received a value equal to (more or less) 7 years of free rent, and debit that from his share of the proceeds, so he is not compensated above and beyond you by getting free rent and 50% of the sale. It is likely that a judge would effectively net the two out against each other and hold that while he may have paid for renovations, he did get free rent; the free rent is his compensation for the renovations; therefore, the proceeds are split 50-50.
The above said, bear in mind that if your brother does not see things this way, he may sue for a larger share. If he sues for a larger share, you will end up likely spending thousands of dollars defending the lawsuit. You may wish to try to compromise: maybe let him get around $5,000 - $10,000 more than you, so that you can move forward without litigation.