I thought the same thing when I purchased bathing suits for example...

Suitcases are significantly more expensive and as such should remain in the home that bought them. How to negotiate that tricky road is another thing...

Are your finances combined?  If so you will have a more difficult time saying no if your OH thinks they can take them. If you think that there will be issues, then you can tell your OH that he is responsible for the cases - transport or replacement is on him. You will not help with $ (hard if combinded expenses), time, or effort related to potential replacement or negotiations.

Suitcases were one of the only things we never had an issue with - clothes, shoes, swimsuits, etc. all an issue.

Tell you that you cant help her out this time. 

Can they be " misplaced"  aka relocated to friend's house so they are unavailable?  
 

If you lend them, she will see them as a gift or returned them ruined.  She can find used ones at goodwill. 

First, are they the kids' suitcases (i.e., gifted to them or purchased by them) or are they YOUR suitcases that are used by the kids when you travel? If the latter, you don't need to make anything of yours available to BM, even for use by skids. What does your OH want to do? Does BM have a tendency not to return things to your house once they migrate to hers?

JUST SAY NO.   It's your suitcases,  you controlled the suitcase. Part of taking kids on vacation is to buy them proper clothing, beach amusement park,  suitcases, suntan, hats.   Just like you did. 

We learned to audit SS's belongings before and after a SperlLand visitation.  If something did not come home with him after Summer, Winter, or Spring visitation, our lawyer sent them a letter demanding the return of the specific items.  They claimed that since they paid CS SS's clothes, etc...were theirs since they paid for them. Ha! The pittance they paid would not cover a single clothes shopping trip for SS each month.  His quality name brand clothing would for some reason not make it back from SPermLand and he would be in Flea Market or Walmart clothing. His nice stuff..... would show up in family pics on his younger sibs over time.

Until our lawyer went shark on them.  Then their crying and victim status would come out and they would hym and haw and whine and cry about how mean we were and how it was not fair that SS had nice things and his three younger also out of wedlock SPermIdiot spawned half sibs by two other baby mamas didn't.

Eventually, SS figured out that his belongings were being stolen and he would keep his bags locked so his stuff would not disappear. That would send SpermGrandHag into bahshee shreeking rages.   As SS progressed into his teens, even the SPermidiot would steal his clothing.

That was when SS started the zero tolerance and bare their theiving asses position he held for the last few years under the CO and has held since then.  He has as close to zero to do with them as is possible.  When there is interface, it usually ends when they try to guilt him into sending money.

The entire time we were under the CO SpermGrandHag would periodically manipulate over something she claimed to have purchased, etc... The first was a car seat she bought for SS when he was an infant. She wanted it back when we married. Um... no. It went to GoodWill when SS outgrew it.  Then... she decided a very nice and expensive winter coat we had purchased for SS needed to be left at casa de SpermGrandHag.  She kept it one Winter visitation and sent SS home in her pink ski jacket from 1979 that was half a dozen sizes too big for SS.  It took a year, but we got it back.  DW picked SS up from winter visitation that year and had SS go into SpermGrandHag's house and bring his coat out to DW while leaving the 20+ yo pink montrosity on SpermGrandHag's bed.  She lost her Hag mind over that.

Though they knew we would tolerate none of their crap, they never completely stopped trying.