I think someone posted that they cleared about $400 million after all debts were paid so that would be their starting point for capital gains ($200 million each), not $950 million. As for their 10% share (5% each), owning an investment is income neutral until they either experience a capital gain or loss when they sell their share. Same concept as owning a business. The capital gains/loss of a business is only a factor when it's either sold or shuts down.
If they have operating cost profits or losses during the year associated with that share, that is calculated as income each year it occurs. If they make a profit, they add it to their annual income. If they have a loss, the deduct if from their annual income. The value of their share is not automatically deducted from the sale price as that was the price for owning 90% of the Sens. The value of their share is $105,555,556 ($950M x 100 [ / 90]), so $52,777,777.50 each and will only become a factor if they sell their share.
I do income taxes for small businesses and rental property owners so I have dealt with this issue, plus I'm a math nerd so numbers are my thing.