Money is tight these days for everyone, so here's a gift idea that can cost you little, except for your time, and also allow you the chance to get closer to your in-laws as well. Are you particularly knowledgeable or skillful in a particular field or activity? Then offer your services in that field in a handmade "Gift certificate" or special invitation.
For instance, if you're a content writer for the web, or knowledgeable in web design, offer to create a website for your mother-in-law, father-in-law, etc. It could be a webpage promoting their business (like the one I designed for my own partner's medical practice.) It could be a Wizzley page spotlighting their hobbies or crafts - especially useful if that person is into trying to sell merchandise on Etsy or build a home business of their own. Or it could simply be a fun personal site or blog, that the person just needs a little help designing and setting up on their own.
Are you good with photo imaging and graphics? Offer to help digitize the family's photo collection so it can be shared and preserved for future generations. An artist? Offer to paint or draw a family portrait - or even a pet portrait, as these are very popular today!
A good cook? Invite them all to a special dinner party in the future in your own home - a great opportunity to build family relations. An avid gardener? Offer to tend to their spring garden, or perhaps create a new seasonal garden or flower bed for them come the summertime. Do your brother-in-law and sister-in-law have young children? Offer to give them a weekend off by having the kids stay at your place, or even just a day off by taking the children to a nearby theme park or kids' activity.
Think creatively at what skills and knowledge you have to share - the possibilities are as endless as your unique talents.