John Gill Reformed Baptist @doctorgill

Therefore in the resurrection,.... As asserted by the Pharisees and by Christ, supposing that there will be such a thing, though not granting it; for these men denied it, wherefore the Ethiopic version reads it hypothetically, "if therefore the dead will be raised"; upon such a supposition, whose wife shall she be of the seven? for they all had her, or were married to her.

Albert Barnes Presbyterian @notesbybarnes

Verses 25-28. There were with us seven brethren. It is probable that they stated a case as difficult as possible; and though no such case might have occurred, yet it was supposable, and in their view it presented a real difficulty.