For which causes can the maaser funds be applied?
Can I help my children to buy a home so that thev can get a smaller mortgage?
Can I help them with repaying thier mortgage?
My children are working and have parnassa to meet their lving expenses and their mortgage payment.
Can I help the costs of the grand childrens education?
Can I help with paying for the education of grandchild with special needs?
Thank you for your question. Let me start by saying how special it is to receive questions concerning the giving of charity – especially where it concerns a parents desire to help their children and grandchildren. May you be blessed with ability to give to your family (and others) in good health and happiness for many long years, and may you receive only "naches" from all your descendants.
There are many opinions about the use of ma'aser kesafim money – but all agree that the money must be used for the poor, or (according to many opinions) for mitzvot. That being so, if your children can afford to buy a house themselves (even though it means paying it off over the course of many years, through a mortgage – as most people do), then you may not use your ma'aser money for buying them a house. Whilst we do allow the use of ma'aser money in order to pay for the wedding and basic needs of marrying off children – this is only to pay for the basic needs of the couple (who could not otherwise afford it themselves), (see Shevet HaLevi, 9, 201). But paying for (part of, or all) of the price of buying a house for your children who can afford it themselves, and therefore are not in the category of poor people, cannot come out of your own ma'aser money. If you want to give them a gift that is a wonderful thing – but it is not charity.
As to paying for education – again it will depend on the situation of the parents. The Torah obligates parents to provide education for their children, and therefore, they are not allowed to use their own ma'aser money for this. However, if they are poor, there are opinions that allow them to use their ma'aser money for the purpose of educating their children. All the more so if they cannot afford at all to educate their children, then others should give money for this mitzvah – and the grandparents are certainly advised to use their ma'aser money for such a need. If the parents want to give their children education above and beyond the standard education – such as sending them to a better private Jewish religious school – then this is considered as a mitzvah that the parents may use their ma'aser money for. In this case too, you as a grandparents could use your ma'aser money for this purpose also.
Concerning the education of the child with special needs is, everything we wrote above is certainly true here also. If the parents cannot afford to pay for the education, or they want to give extra above the standard education, then ma'aser money may be used.
The reason for this is that the child in question is poor (assumingly) and when the parents cannot afford to pay for their obligation to educate the child, or there is a desire to educate the child beyond the minimum requirements, then the child needs to receive charity, for which ma'aser money may be used.
I hope this short outline will be of help to you.