MIL holding my dog hostage

Some background first: my in laws are very old fashioned folks. They’re not that old though, having had my husband when they were only teenagers. So they still lead fairly active lives and work. They are very traditional, and one old fashioned belief they hold closely is that everyone should be visiting them, and they don’t have to visit anyone because they’re “old”. They maybe visit our home 2 hours away once a year, so they don’t really have a close relationship with my kids. They expect us to visit them several times a month and complain when we don’t, but we have very busy schedules ourselves and simply don’t have that much free time. They have much more free time to travel to see us because they don’t work full time, only part. They fuss and moan about us not ever visiting them but they make zero effort to ever see us or our kids. And personally I don’t feel like it’s my responsibility to make them have a relationship with my kids 🤷🏽‍♀️

So this past week my husband and kids and I went on a vacation. We asked them if they would babysit our dog at their house (they love animals, have a huge yard, so it was an automatic yes. We agreed on Thursday (today), they would drive her back for us since we have been traveling and are exhausted). Well they did not show up with our dog today and they are saying if we want our dog back we need to come see them and stay the night. My husband told them we can’t, he’s got to get back to work, and plus since we’ve been away from home for awhile we just want to stay at home anyway. His mom got pissed and said “well then I’m keeping Luxley (our dog) until you come over” and hung up.

We honestly don’t have the time or energy to travel 2 hours there and 2 hours back until NEXT WEEKEND meaning she’s functionally holding my dog hostage for over a week. I really miss my dog and want her back. They both agreed they would drive her back to us and now they’re saying they won’t. What would you do?! Do I really have to wait a whole nother week to get my dog back? 😔