Question on Select field Limit Submissions

Hello,

I am developing a registration form where registrants can reserve either 1 or 2 tables subject to availability. In the past, I have used the Select field and have limited submissions. But in this case, I would have 2 options in the Select field dropdown.

1. Reserve 1 table
2. Reserve 2 tables

The problem is that the 2 options are both draining the same capacity which is 20 total tables. For example, if I have 5 submissions for 1 table and 2 submissions for 2 tables, then a total of 9 tables out of 20 have been reserved (5 + 2*2 = 9).

Is there a way to have the Select field combine the totals from both so we don’t exceed our capacity?

Alternately, I have also thought of allowing the registrant to select multiple fields in the Select dropdown like this:

1. Reserve 1 table
2. Reserve a 2nd table

If they selected both fields then the capacity would be decreased by 2, i.e. count both as part of a single submission.

Is there a way for me to accomplish this requirement using the Select field or do you have a different suggestion? Alternately, do you have some mu-plugin code that you have previously developed for another user of your product for a similar purpose?

Thank you.