From your description and diagram I’m guessing this is a relay module with opto couplers. 17ma is quite high for a trigger current. You may be able to use a single transistor to simultaneously switch both pins (IN1 and IN2) and Vin to minimize the number of connections if that is your goal. You may be able to experiment with series resistors to reduce the current and still get clean switching.
If, however, you want to tie output pins together, you can get some ideas from this: power - Can I use two Arduino digital pins in parallel to keep a higher voltage? - Electrical Engineering Stack Exchange
Use direct port manipulation to ensure simultaneous switching.