That character combination can work well.
The warrior can pick up some other skills that don't rely on high intelligence (like summons, buffs) or dexterity (that can be boosted later with equipment bonuses).
A point in Aerothurge would give access to Teleportation and Thunder Jump (the stun effect wouldn't trigger as much with a low intelligence, but it gives a relatively low AP way to get into the thick of battle). A point in geomancer would give Midnight Oil (slow opponents, or set up for fire surfaces and smoke clouds), Boulder Bash (no line of sight required) and the spider summon. The scoundrel skills Walk in Shadows (invisibility), Winged Feet (lets the character walk over surfaces unaffected) are useful in and out of combat, and Fast Track and Trip could be useful (more so after getting some dexterity bonuses); the adept skill Cloak and Dagger (teleport) can also be handy.
The mage should probably look at getting 1 or 2 levels in Witchcraft and the elemental schools, with 1 or 2 at level 4 or maybe 5 (if they have more than 1 compelling master spell, or for a talent requirement).
With Lone Wolf characters, being disabled is more of a problem than a full party, so consider boosting Willpower and Bodybuilding. This can be be done with equipment bonuses, or equipment, talents and traits can grant immunity to certain CC effects. Summons can also help, drawing at least some of the attacks which would otherwise be directed at your main characters.
At least hang on to any equipment you find with crafting or blacksmithing bonuses. You don't need to craft equipment or potions, etc, but it can be quite helpful.
Divinity: Original Sin Enhanced Edition Character/Party GuideTactician/EE/Advanced Guide - even playing on tactician, you don't need to min/max as much as this guide suggests
Earning a honest living (newbie friendly)