I feel mother of your husband is tool old. As you feel lonely for your children she might be feeling the same way for her child. If any of your son wants to live with you for some time you would expect your daughter-in-law to help in doing so.
In my opinion, you may go with your husband for 4-5 months while applying for leave. You have not discussed the matter yet with your husband but you should do so.
As far as this kind of migration is concerned, I can't clearly state whether it is same migration as migration in the cause of Allah. However, if you go to help your husband in his visit, it will be a benign thing.
However, I request the learned visitors to shed light on this problem to find a solution which is acceptable in Islam.
