It's a pity you didn't change the locks after your DH passed away, if you knew that your SD had a key, and might be liable to pull such a stunt.   Personally, if I were friends with their mother and wanted to preserve this relationship, I'd write the tools off, but get the locks changed straight away so that nothing like this happens again.  If you really want the tools back and it's a matter of principle, get a lawyer to send your SD a threatening letter. 

I wonder if it’s possible the mother knows what they are doing (although admittedly parents of grown up kids don’t always know what they are up to).

I agree with Kes about getting a solicitor. 

I am surprised they had a key to get into your house. Change the locks like Kes suggested if you want to save yourself a whole lot of heartache. Oh, and surely that must be theft...

I am not sure why you feel the need to speak to them with the way they treat you. You don’t ‘have to’ if you don’t want to. 

Call the cops. She entered your home without permission and took your belongings.

Call the police. You were robbed. She had no right to take those tools from your home.

I agree with the other who suggested you call the police. You were robbed. File a report.

Do you have any correspondence saved between you two regarding the tools? Was there and inventory list?

I would say file a police report and take her to small claims court, but ONLY if you have supporting evidentiary proof. Attorneys, judges and police deal with the black and white facts .

How horrible. Best wishes.

Sorry for the loss of your DH. Did he have a will specifying who is to have what ?

I'd call the police. She broke into your home, stole tools that she knew were not hers. This is a crime. 

Agree with everyone else. That is truly shitty behavior. Skids tend to feel entitled to anything and everything "daddy" touched...completely disregarding next of kin laws, the fact that SM contributed to the bills and maintenance of the household for decades...

To them it's all "daddy's stuff" which means it's THEIR stuff and you're keeping it from them. 

Fortunately the law is not on their side. You were his life partner, and anything that wasn't left to them specifically is yours. End of story. You've already been more than generous giving her his Porsche and golf clubs...and this is how she repays you? 

Hell no. Take your power back. Document the correspondence...write your narrative...gather any information you may have (the other SD bringing back the duffel is also evidence...take pictures of what was brought back.) 

Then file a police report and take it to small claims. And yes...definitely change the locks and get more home security ASAP.