Assuming two use years, I see banking/borrowing to have one reservation and making separate reservations and linking them as about equal overall. It'll be slightly easier to reserve if you bank and borrow and do a given villa from one master contract but you'll have the risk of the banked/borrowed points if you have to change or cancel. Using two contracts for a single reservation and linking will be a little safer but you'll have to check in again midstay. But since you're looking at multiple villas at one time you can reserve an entire villa from each contract, minimize the extra work and the risks of both mid stay checkin and banked/borrowed points.
Given the smaller contract, I MIGHT change my recommendation to buying a single larger contract and selling the smaller one. IF one were going to do this I'd only do so in the following way. Look for the perfect larger contract that's loaded and a good price, buy it for cash and then sell the 100 pt contract at a higher price. To me one would need to be able to float both contracts for cash to make it reasonable to do so. That's esp true if one were thinking of a second smaller contract of under 150-170. So owning a smaller contract and having a poor UY, it very well might be better to sell and rebuy if one is upgrading contract size enough to take advantage of the inherent price differences there. To use round numbers, selling a 100 pt contract at $60 a point and paying commissions will net roughly $5400. Buying a second 100 pt contract at $60 will cost maybe $6500. Buying a 200 pt contract at roughly $50 will cost $10500 minus the $5400 to end up at an additional $5100. I'd ignore dues for the comparison because they should end up canceling out if all else were equal.
Go stay there first during this time before you commit. You might also consider trying a different resort option at the same time to make sure you have the most info possible. Lastly, anything other than prime summer isn't too difficult for HH so a non HH
DVC option might give you different options.