Looking to give my players some buffs, need advice

Hey all. I'm currently running Phandelver and Below: The Shattered Obelisk, and I am interested in giving my players some buffs for the upcoming dungeons. I only have 2 players, so I wanted to scale them up rather than scale the enemies down. Here is the current layout of my characters:

Drow Bard/Sorcerer multiclass. Lived in the Astral Sea for a while after escaping the Underdark and dislikes drows and aberrations. He has been the party's de-facto leader since he's the best at persuading and decieving the enemy into letting them into their stronghold. Predominantly uses Magic Missile or Phantasmal Force depending on the situation. He mostly has the typical weaknesses involved with playing a spellcaster, especially since he casts Shield a lot during combat.

Half-Elf Cleric who worships Wario. I've leaned into the joke by mentioning how Wario gives him insight into finding treasure, and also causes enemies to scream like Wario when they are defeated. He's the frontline of the two because of his high AC and preference towards melee combat. He likes to use a boat oar he found and typically uses Spiritual Weapon and Inflict Wounds for spellcasting. However, his HP is absolute garbage since he has a 10 in Constitution, but is a powerhouse outside of that.

Overall, I'm looking to buff them to the point they have the offensive potential as if they had an additional party member on their team (we used to have a third player, a barbarian, but he's since left).