The invisibility spell states:
A creature you touch becomes invisible until the spell ends. Anything the target is wearing or carrying is invisible as long as it is on the target’s person. The spell ends for a target that attacks or casts a spell.
When you cast this spell using a spell slot of 3rd level or higher, you can target one additional creature for each slot level above 2nd.
Can you upcast the invisibility spell to make a small group invisible but still able to see each other?
The description from the invisibility spell states that the affected targets are invisible so that really is all it does. This is commonly known as spells only do what they say they do.
If the Invisibility spell allowed a mode where targets were invisible but able to see each other this would have to be included in the description of the spell.
In order for targets to see each other while invisible, you would need something else, for example, the True Seeing spell cast on each of the creatures . Since true seeing is not a concentration spell, you could maintain everything at the same time (though it will probably cost you a lot of spell slots)1.
1. Suggested by NautArch
