I completely understand your fear. Maybe have your vet order regular frontline not the plus. Crimson was 1.6lbs when I started using frontline plus on her. I never let them give Crimson more than 1 vaccine at a time either. Hiring in a pest control person while you take Sophie away for the day sounds like a better thing for you. I don't know how often they would have to come but could imagine more then a couple.
I hope, someone chimes in with other responses that way I can read them.
Keep me informed on what you decide. Good Luck!