All amounts, no matter how little are reportable income.
" I’ve been told if we split it we don’t have to claim it because it’s so small" only means that the people who paid you don't have to issue a 1099-NEC, if it's under a certain amount (usually $6000. But, you still have to report the income, no matter how little.
The one who got the 1099-NEC reports the whole $710, then claims a deduction for the half the other person got. Then the other person' reports his half. For simplicity, you may want to not take the deduction, so the other person doesn't have to report it.
Technically this should be filed as self employment income, meaning you have to pay social security and Medicare tax, in addition to income tax. But, if this was a one time gig, you can report it as "other income" (it's harder to take deductions for other income). At least one of you needs to file an amended return, to report the income. Wait until your first return is fully processed.
