Yeah, was he invited? How well do you know them? Is it a dog you share with the boyfriend/ their son? Do you live together with this pet?
If they have a rambling yard and their dogs like other dogs and your dog doesn't chase their cat, then sure go ahead and ask your boyfriend if he would ask his parents. If it is a first visit I would just say "NO" and see how you all get along without the burden of needing to look after your dog.
I have a dog who is a sweety but is very territorial with other dogs. I have also had other peoples visiting dogs kill my chickens on an overnight... Not fun. I appreciate that most people have better behaved dogs than I have, but I would rather enjoy your company than worry about how my dog will behave with your dog. Let the relationship develop or wait for them to say " why don't you bring your dog along".