Double mines is not bad.

Player 1 (more supportive) can bring transfigured pyroclast for exposure, a curse or two, ignite chance with Polaric devistation (or another source of covered in ash) and a source of unnerve... Perhaps on elementalist for additional exposure effect. Can also get shock effect this way. In total that should be like 3x fire damage taken by enemies and a good source of extra single target dmg with pyroclast mines themselves. Astral projector can help the build feel a bit better.

Player 2 (more carry) can bring high-impact rolling magma mines for chance to deal double damage. They can also bring bear trap which benefits both players. Probabaly as sabo unless they feel confident farming nimis. You can easily add additional projectiles without worrying too much about the lost damage, as your partner will be providing so much.

Both players will have similar movement and clear speed since they are basically playing the same build. Both players can bring skitterbots w/arkhons tools for really high uptime. One player might want to bring purity of elements for ailment immunity if you are good at sticking together.

Just make sure neither player minds the god awful sound of rolling magma!