In all these examples, I think you should ask your lawyer what is customary in your state/area because that will give you an idea of where there is room for negotiation and where you (or he) are completely in the right.
But here's my personal opinion on your questions...
1. So, WH very often traveled for work. He has barely traveled at all since Covid, but I think it's reasonable to expect that he really could travel again at any time. I had it put in the Separation Agreement under Child Custody, that if either of us travel for work during our regular custodial time, we are not entitled to make-up time unless mutually agreed upon in writing. He's come back with wanting to be compensated for a percentage between 25% - 40% of the time he would miss with the kids when traveling for work.
The pros of being flexible with him about this issue are (1) you might need him give you some leeway in the future as well if you need to informally modify any parenting time arrangements and (2) as you move from a dual-parent household to a single-parent household, you're going to need that make-up time just to have a break or get things done.
The cons are (1) it puts you in the position of having to rearrange your life according to his availability, (2) the kids are teenagers and they are going to have their own plans and commitments that could potentially be disrupted by this, and (3) you would have to be really diligent about tracking the days you give him to makeup the time so you can't be accused violating the agreement.
2. He says there needs to be a statement that neither party may discuss the terms of the separation with the children at any point
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I don't think you should agree not to discuss the terms of the separation agreement. There are certain things that your kids will need to know about, such as why they're spending x days with dad and y days with you.
If he's concerned about you bad mouthing him, you can agree to add a non-disparagement clause to the agreement, which achieves essentially the same thing but doesn't refrain you from speaking about the practicalities of life that are covered in the agreement.
3. According to my lawyer, the standard child custody schedule is 2-2-5-5. WH says that's too much back and forth for the kids and would prefer a 7 day schedule. What are your experiences with schedules that work best for your kids at this age and why?
I agree with him on that point, but I also think that your kids are old enough now to have their opinions factored into this part of the agreement. Do they prefer the convenience of the 7-day schedule (since there's less frequent back-and-forth between homes) or do they not want to go more than 5 days without seeing their other parent?
BW, 40s
Divorced WH in 2015; now happily remarried
I edit my comments a lot for spelling, grammar, typos, etc.