Each child should apply to schools that are affordable with merit and/or need based aid.
The ones with lower stats might have to apply to instate schools and/or less selective/lower ranked ones.
Explain the savings that existed before/after the marriage for each of them.
Let’s say you had saved $40,000 per triplet and your H saved $40,000 for his D.
Since the marriage you saved another $40,000 per child.
So now each has a $80,000 budget for four years.
That would give them $20,000 a year, plus what the dad of the triplets would contribute per year.
If they pick a school with that budget (instate or OOS/private with merit and/or need based aid) they might not need to borrow their student loan, otherwise they can increase the budget by the $5,500 they can borrow.
The stepdaughter can get high merit and scholarships and wants to be close to late mom’s family. Hopefully that is in the budget, plus what her dad can contribute from the house sale.
If there is extra money, it should be saved for her.
Keep in mind, that the dad of the triplets might stop helping to pay in future years if he gets remarried, finances change etc, so the triplets might want to pick a school that is affordable without their student loan, so they can keep going to school if their dad should stop paying.