How do I cope with my fraying patience towards my caregiving situation?

Roxlang, don't ever feel ashamed for feeling overwhelmed. Is FIL mentally with it? If so you and hubby need to set him down and come up with an action plan. Get a potty chair to put beside his bed for night time use. A baby monitor by his bed will help you hear if he needs assistance during the night.
You need to schedule time for you and hubby and also time for you,hubby and your little angels.
Does hubby have siblings? Friends?

My fil has parkinsons and diabetics not to mention a stroke 2 yrs go. He is a very pleasant man. I just which there is more of me to give. Sadly I have only been doing this since March of this year. My husband (his son) hardly getts any sleep either because of the pd fil falls all of the time because he refuses to ask for help.

I've felt like i've had enough nearly every day. And I've also been ashamed for it but i think this only sabatoges my abilities. You have your hands full and must be feeling overwhelmed. My county has a department of aging that offers support for caregivers. I urge you to call them.

It's unknown how old your FIL is or his physical/mental condition. He may qualify for help from visiting nurses or even hospice if he meets their criteria for help.

You say you're the sole caregive and he's your FIL. If your husband is in the picture, you need to let him know and you two can explore the possibility of another living arrangement for your FIL. As caregivers, we are in the driver's seat and we can make decisions for our parents to ensure they are receiving wonderful care, even if it's not in our home.

Please call until you find someone who can help you. There are agencies out there who understand what you are facing.

Well I agreed to it, because we own a home and have the room but I didn't expect not to recieve help.

I don't think there's anything wrong with the way you feel. I think it's a natural reaction for having to care for your babies, and FIL. Why is he your responsibility? It seems no one respects the sanctity of motherhood anymore. What two precious blessings you have. They need their mommy. I find my nine year old missing out because of two distracted parents caring for 3 elderly parents. It is taking its toll on all of us. Many days, I feel as though I've had "enough" of some of it, too. I long for the freedoms I had when it was just me as wife and mom. You are normal. Seems like you need some help! Take care, and I hope you find a solution that works for all of you.