Maybe it´s because of the floor lamp and the ceramic vase, do you have them?
In my case I´m level 27. Sign at level 26, lamp at 41 and vase at 32, and when reaching 5k levels i get around 400k shares per reset with gems, i usually wait more before reset cause i don´t mind it but... i don´t get that much shares.
How many levels do you have when you are selling? A level 25 sign is a x5 multiplier to your shares. Assuming you two are selling at a similar level then their sign is around level 50 for a x10 multiplier instead of a x5. Though that probably isn't the case as my sign is only level 44 and I'm level 195, so I doubt a level 46 has a level 50. If your signs are a similar level then the they would be selling with around twice the levels you are. Most likely you just don't have as many levels when you sell your company as them. They probably have a higher overall multiplier as well. So they are able level up their girls faster and as a result get shares faster.
Extremely important ever since they added the leveling system to them. Get a high enough multiplier and all future multipliers become lager. I never spend gems on anything else, so I'm at multiplier level 8 with an x1.2m multiplier, and the 300 gem purchase gets me an additional x781.5k multiplier.