Puppy arrives tomorrow, he's had first jabs only, can I...

[Furminator]

take him to my IL's house on Monday where my SIL will be with her (fully vaccinated) dog?

yes, but dont walk him in street or meet dogs you dont know if they are vaccinated or not.

Thank you :-)

When we got our new puppy I was advised by the vet not to take either the puppy or our existing dog (fully vaccinated) out until the puppy had its second jabs. I'd give your vet a quick ring and check with them if I was you

It will be fine. Don't bother with ringing the vet.

As long as you don't let your dog walk on the pavement and to only socialise with other, known vaccinated dogs in areas where unvaccinated dogs have definitely not been, he'll be fine. And able to benefit from very valuable socialisation too.

As daisy said.