1. If there are six big trucks, then 45*6=270 people, so there is no small truck, so there is no such situation.
2. If there are five large trucks, 1 minivan, please note that "the travel society arranges tourists to fill the bus first, and then fill the minibuses in turn, and the last minibus must have at least 20 seats even if it is not full", so the number of minivans must be greater than 2. Therefore, it does not exist.
3. If there are 4 trucks and 3 minivans, there are 4 * 45+3 * 90 = 270 > 253 people. And 4 * 2+3 *1=11is consistent with the number of doctors, so it is established.
4. If there are three trucks and four minivans, there are 3 * 45+4 * 30 = 255 > 253 people, but 3*2+4* 1= 10 people, which does not meet the number of doctors, so it is not established.
5. If there are two big trucks and six small trucks, the same is true at this time.
6. Large trucks 1 and 7 small trucks are temporarily suspended.
To sum up, the scheme (1) rents 4 buses and 3 buses; Scheme (2) Rent 2 buses and 6 minibuses.