I don't think we can assume any "of course" here. For one thing, we have no verification that a trial is in the offing for the WM murder charge. No announcement has been made. In the LB case, if both the accused are found guilty of first-degree murder in this case, it is likely the Crown will reconsider the cost of a trial and may entertain some kind of plea deal with the accused in that case. If the accused are already sentenced to life, there is no further "time" to be added to that sentence, as convicted murderers are never entitled to release. Sentences such as those in the USA for 750 years and so on are ridiculous.
Now, if the accused had been first convicted on a lesser charge (as happened in the David Snow case - you can Google it, or see a brief summary here:
https://www.thestar.com/news/insigh...-the-memoirs-of-an-opp-criminal-profiler.html), the Crown would proceed with a murder trial to follow. The LB case I would also expect to go to trial if either or both of the accused are acquitted (very unlikely) or convicted of a lesser offense.
But if both get the maximum sentence in this case, there would be serious thought about alternatives to proceeding with two more murder trials and other options would be considered.