I agree with
@SouthFayetteFan. If your DH is starting at 0/24 and only 30% CL to income, there's no issue doing the CSR+CSP double dip first.
As you said, getting the CSR will give you access to that card's 1.5x UR redemption bonus, and your household can make it a habit to move all UR points to the CSR after they post at the end of each UR-earning card's statement (given rumors Chase may eventually restrict points pooling).
@miztressuz already pointed you to some tips on pulling off the CSR+CSP double dip.
Some additional thoughts on your DH's applications: DH has about 20%+ worth of income "runway" that can be extended as credit by Chase on the two cards. That should be plenty of room. However, since you want the CSR more and should apply for it first, just know that everyone who's been approved for the CSR is incredulous at how much credit they're given on the CSR. Like $20-30k+. It's crazy. That could affect how much more credit Chase is willing to extend to DH on the CSP. Most people seem to apply for the CSR then the CSP, which is why most DPs about having to call in on the second card seems to be about moving credit around. If you need to reallocate some credit to open the CSP, move it from DH's Freedom with the crazy high limit (don't mention the CSR you just got approved for).
If you do the CSR+CSP double dip first, you should put off referring the CIP for 4 months, like
@SouthFayetteFan suggested. Slot the Amex Hilton Biz 125k offer in next month for DH, so his timing looks like:
5/18: CSR+CSP
6/18: Amex Hilton Biz
9/18: CIP (via referral)
If DH and you are both getting the Amex Hilton Biz, plus the CSR+CSP, that's a combined $18k MSR in the next 4 months, which hopefully should keep you busy until September.