Opposition in JS and Article 70

The JP having members in both the government coalition and the official opposition raises questions around Article 70 of the Constitution which states that MPs voting against their own party must resign from their seats. For example, a bill comes up for vote in the JS. The government members of JP vote in support, but the opposition JP members vote against. Is Article 70 violated, and if so, by whom?  The government MPs voting against the party they belong to (JP) or opposition MPs voting against the coalition their party belongs to?
The JP is a pretty tame opposition, illustrated when they set the bar at only opposing anything the government proposes that is “anti-people”.   Legislation that is not “anti-people” may still need opposition to amend if not necessarily to stop it. The risk is the government could use the threat of Article 70 to keep opposition members from performing the role they need to play.