Wa alaikum salaam wa rahmatulahi wa barakatuh sister,
This is indeed a difficult situation to be in. You and your child are apart from your husband due to problems with his parents, but now, understandably you are missing him dearly, but his father seems to be standing in the way of this happening.
Naturally, it is best for the father and mother to be together for a number of reasons; firstly as a protection for one another as described in the Qur’an. This is a type of protection that cannot be fully obtained by living apart. Also, for your daughter, it is the most ideal to have her father around for the purposes of building bonds and giving you support as well as giving her a sense of security.
However, at the same time, with your father in law seemingly placing potential restrictions on this it may prove difficult to move forward. Obviously, in line with Islamic principles, it’s not advisable to just cut ties with his father and disregard his opinion entirely, but on the other hand, he is standing in the way of your families happiness. It is therefore important that you approach this situation carefully in order to uphold family toes and not upset his father, whilst also striving to reunite your family.
Given that there are underlying circumstances that led to this situation arising in the first place, it might be advisable to address these issues first. In which case you and your husband could approach them together and sit calmly to discuss the matter. Of there’s any chance it might get heated, it might be best to make sure to arrange a date in advance so that it doesn’t come as a nasty surprise to them. It is also advisable to invite a neutral party who you can all trust, such as your local imam to be present at this meeting. He will be able to observe things from a neutral perspective and advise accordingly, whilst keeping in line with Islamic principles.
Any conversation that you have with them remember to remain calm without using harsh words and they will be more likely to hear what you have to say and react with softer hearts. Let them know how it is affecting your life as well as their grandchild. Let them understand the situation from your perspective. If they speak harshly with you, again, try to remain calm and respond calmly. This can also help to calm their arousal levels also. Even if you feel that they are wrong to do your best to treat them with respect as you would your own parents. It may well be that unless they are being completely unreasonable that you agree to disagree and allow them to feel like they are to the right if this means that they will back off and allow your family to be together again. It may feel like this is in just, but remember that Allah is the ultimate judge and will judge their actions accordingly so you can feel more content that ultimately His judgment will prevail and this will save you potentially getting into a heated argument that may lead to even worse circumstances. Once you have overcome this stage you can gently work in rebuilding positive relations with them again.
Continue to pray for them; that Allah will soften their hearts and that you will be reunited with your family again. This will also serve as a means to soften your own heart towards them also allowing you to approach them respectfully and calmly, and more likely to yield positive results for all.
May Allah soften all of your hearts to one another and promote happiness and contentment between all parties. May He reunite you and your husband once more in love and happiness.