I believe the limit of 3 different loans is still current. Again, you would need to check to be sure.
When we originally purchased we already had both a house mortgage and a loan on an RV. We were not allowed to also declare the interest on the Disney DVC as it was a 3rd property.
At the time, you could have only two and if I recall, all the following counted:
A home's primary mortgage
A secondary mortgage
A home equity loan
A loan on an RV (if fully contained - having sleeping, cooking, bath facilities)
A loan on a Boat (if fully contained - having sleeping, cooking, bath facilities)
A loan on a vacation home, etc.
In our case, we went and got a home equity loan, paid off the RV loan and paid off the DVC loan using the equity loan. That put us at only two: Main home mortgage and home equity, so everything from then on was deductible, and the home equity loan was at a lower rate, so everything worked out great.