If you keep paying on the 1st mortgage but are behind on your 2nd, can the Bank holding the 2nd mortgage foreclose??

Sometimes. Depends on local laws and the wording in the contract. However, if they do force a foreclosure, the primary lienholder gets paid first.

Normally yes they will be able to

Yes

The first, as the name implies, has FIRST right to recover.

A junior mortgage holder can foreclose on your home, however, they would need to gave first position by buying out the senior lien holder. Most junior lien holders will not pay off a senior lien holder unless you have allot of equity in this property. A foreclosure can cost several thousands of dollars to process and unless the junior lien holder can recover their balance, plus the first mortgage pay off, and legal fees, they typically will not foreclose the property.

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I recommend that you seek professional legal advise from a real estate attorney in your state. I am not a attorney and I only offer you my opinion and not legal advise.