One effective strategy will be to, as much as possible, pay third parties directly for goods and services to be provided. Regarding the cash allowance, dividing it into smaller, more frequent payments might help. Meeting the needs for socialization through a day program might justify limiting contact with the boyfriend, but unless the theft and overreaching is limiting your ability to meet your ward's needs, it might not be necessary to eliminate that contact.
Best wishes for an outcome you can accept, and please remember to designate a best answer.
This answer is offered as a public service for general information only and may not be relied upon as legal advice.
I would recommend limiting the direct payment of cash to both individuals so that they have less money on hand at any given time. You may consider asking for receipts in order to increase the amount- this level of accountability may scare off the boyfriends or open conversations with them about how much/why they are spending money on these people. Any family and/or mental health providers that you have contact with could back you up on these type of conversations.
If you feel actual theft is occurring, you may want to contact the police on his/her behalf. Even if charges are not pressed, a police officer would be assigned to investigate and may scare off the individuals from taking further advantage of your wards. Any threats of physical harm or physical harm to a mentally challenged individual should also be reported. Many state offices (police and prosecutors) have special units designed to protect your wards.
You may want to suggest your wards going to local day centers and/or mental health groups. These are free services and would help your clients feel less lonely. They may also connect with an advocate who could address the issues you outline above.
This comment is provided for informational purposes only, and is not to be considered legal advice and/or the establishment of an attorney/client relationship.