The type of people who ask these questions about the differences of Guru Sahib are usually people from the Radha Swami Cult or other cults with the same agenda. I have learned through experience that its best to avoid socializing and exchanging Gurmat with such unworthy people. I was once talking to a Radha Swami person , and I know how much they cant stand Dasmi Paatshah. I kept saying "Sri Guru Gobind Singh Ji" "Sri Guru Gobind Singh Ji" .. to him , and he finally got annoyed and asked me why do you keep saying his name I replied because his name seems sweet to my tongue, he tryed to be smart and asked me doesn't the other Gurus name seem sweet? I replied," Yes" there is no difference between Guru Sahiban my masters name seem sweet to me, and he stayed quiet and decided to find some other way to undermine Sikhi. He then asked me " how did Guru Nanak go to Mecca if he was not Muslim". After my reply he try to find some other fault in Sikhi, and he kept going on and on. ITs best just to avoid these people they have such bad fortune and they try to pollute others around them. If someone is genuine in asking such questions then you should refer them to the following verses in Bachitar Natak
ਚੌਪਈ ॥
ਤਿਨ ਇਹ ਕਲ ਮੋ ਧਰਮੁ ਚਲਾਯੋ ॥ ਸਭ ਸਾਧਨ ਕੋ ਰਾਹੁ ਬਤਾਯੋ ॥
Guru Nanak spread Dharma in the Dark age and put the saints on the path.
ਜੋ ਤਾਂ ਕੇ ਮਾਰਗ ਮਹਿ ਆਏ ॥ ਤੇ ਕਬਹੂੰ ਨਹਿ ਪਾਪ ਸੰਤਾਏ ॥੫॥
Those who followed the path propagated by him, were never harmed by the vices.5.
ਜੇ ਜੇ ਪੰਥ ਤਵਨ ਕੇ ਪਰੇ ॥ ਪਾਪ ਤਾਪ ਤਿਨ ਕੇ ਪ੍ਰਭ ਹਰੇ ॥
All those who came within his fold, they were absolved of all their sins and troubles,
ਦੂਖ ਭੂਖ ਕਬਹੂੰ ਨ ਸੰਤਾਏ ॥ ਜਾਲ ਕਾਲ ਕੇ ਬੀਚ ਨ ਆਏ ॥੬॥
Their sorrows, their wants were vanished and even their transmigration came to and end.6.
ਨਾਨਕ ਅੰਗਦ ਕੋ ਬਪੁ ਧਰਾ ॥ ਧਰਮ ਪ੍ਰਚੁਰ ਇਹ ਜਗ ਮੋ ਕਰਾ ॥
Nanak transformed himself to Angad and spread Dharma in the world.
ਅਮਰਦਾਸ ਪੁਨਿ ਨਾਮੁ ਕਹਾਯੋ ॥ ਜਨੁ ਦੀਪਕ ਤੇ ਦੀਪ ਜਗਾਯੋ ॥੭॥
He was called Amar Das in the next transformation, a lamp was lit from the lamp.7.
ਜਬ ਬਰਦਾਨਿ ਸਮੈ ਵੁਹ ਆਵਾ ॥ ਰਾਮਦਾਸ ਤਬ ਗੁਰੂ ਕਹਾਵਾ ॥
When the opportune time came for the boon, then the Guru was called Ram Das.
ਤਿਹ ਬਰਦਾਨਿ ਪੁਰਾਤਨਿ ਦੀਆ ॥ ਅਮਰਦਾਸਿ ਸੁਰਪੁਰਿ ਮਗੁ ਲੀਆ ॥੮॥
The old boon was bestowed upon him, when Amar Das departed for the heavens.8.
ਸ੍ਰੀ ਨਾਨਕ ਅੰਗਦਿ ਕਰਿ ਮਾਨਾ ॥ ਅਮਰਦਾਸ ਅੰਗਦ ਪਹਿਚਾਨਾ ॥
Sri Nanak was recognized in Angad, and Angad in Amar Das.
ਅਮਰਦਾਸ ਰਾਮਦਾਸ ਕਹਾਯੋ ॥ ਸਾਧਨ ਲਖਾ ਮੂੜ੍ਹ ਨਹਿ ਪਾਯੋ ॥੯॥
Amar Das was called Ram Das, only the saints know it and the fools did not.9.
ਭਿੰਨ ਭਿੰਨ ਸਭਹੂੰ ਕਰ ਜਾਨਾ ॥ ਏਕ ਰੂਪ ਕਿਨਹੂੰ ਪਹਿਚਾਨਾ ॥
The people on the whole considered them as separate ones, but there were few who recognized them as one and the same.
ਜਿਨ ਜਾਨਾ ਤਿਨ ਹੀ ਸਿਧ ਪਾਈ ॥ ਬਿਨ ਸਮਝੇ ਸਿਧਿ ਹਾਥਿ ਨ ਆਈ ॥੧੦॥
Those who recognized them as One, they were successful on the spiritual plane. Without recognition there was no success.10.
ਰਾਮਦਾਸ ਹਰਿ ਸੋ ਮਿਲ ਗਏ ॥ ਗੁਰਤਾ ਦੇਤ ਅਰਜਨਿਹ ਭਏ ॥
When Ramdas merged in the Lord, the Guruship was bestowed upon Arjan
ਜਬ ਅਰਜਨ ਪ੍ਰਭੁ ਲੋਕਿ ਸਿਧਾਏ ॥ ਹਰਿਗੋਬਿੰਦ ਤਿਹ ਠਾ ਠਹਰਾਏ ॥੧੧॥
When Arjan left for the abode of the Lord, Hargobind was seated on this throne.11.
ਹਰਿਗੋਬਿੰਦ ਪ੍ਰਭ ਲੋਕਿ ਸਿਧਾਰੇ ॥ ਹਰੀਰਾਇ ਤਹਿ ਠਾਂ ਬੈਠਾਰੇ ॥
When Hargobind left for the abode of the Lord, Har rai was seated in his place.
ਹਰੀਕ੍ਰਿਸਨ ਤਿਨ ਕੇ ਸੁਤ ਵਏ ॥ ਤਿਨ ਤੇ ਤੇਗ ਬਹਾਦਰ ਭਏ ॥੧੨॥
Har Krishan (the next Guru) was his son; after him, Tegh Bahadur became the Guru.12.
ਤਿਲਕ ਜੰਵੂ ਰਾਖਾ ਪ੍ਰਭ ਤਾ ਕਾ ॥ ਕੀਨੋ ਬਡੋ ਕਲੂ ਮਹਿ ਸਾਕਾ ॥
He protected the forehead mark and sacred thread (of the Hindus) which marked a great event in the Iron age.
ਸਾਧਨ ਹੇਤਿ ਇਤੀ ਜਿਨਿ ਕਰੀ ॥ ਸੀਸੁ ਦੀਆ ਪਰ ਸੀ ਨ ਉਚਰੀ ॥੧੩॥
For the sake of saints, he laid down his head without even a sign.13.
ਧਰਮ ਹੇਤਿ ਸਾਕਾ ਜਿਨਿ ਕੀਆ ॥ ਸੀਸੁ ਦੀਆ ਪਰ ਸਿਰਰੁ ਨ ਦੀਆ ॥
For the sake of Dharma, he sacrificed himself. He laid down his head but not his creed.
ਨਾਟਕ ਚੇਟਕ ਕੀਏ ਕੁਕਾਜਾ ॥ ਪ੍ਰਭ ਲੋਗਨ ਕਹ ਆਵਤ ਲਾਜਾ ॥੧੪॥
The saints of the Lord abhor the performance of miracles and malpractices. 14.
ਦੋਹਰਾ ॥
DOHRA
ਠੀਕਰਿ ਫੋਰਿ ਦਿਲੀਸਿ ਸਿਰਿ ਪ੍ਰਭ ਪੁਰਿ ਕੀਯਾ ਪਯਾਨ ॥
Breaking the potsherd of his body head of the king of Delhi (Aurangzeb), He left for the abode of the Lord.
ਤੇਗ ਬਹਾਦਰ ਸੀ ਕ੍ਰਿਆ ਕਰੀ ਨ ਕਿਨਹੂੰ ਆਨ ॥੧੫॥
None could perform such a feat as that of Tegh Bahadur.15.
ਤੇਗ ਬਹਾਦਰ ਕੇ ਚਲਤ ਭਯੋ ਜਗਤ ਕੋ ਸੋਕ ॥
The whole world bemoaned the departure of Tegh Bahadur.
ਹੈ ਹੈ ਹੈ ਸਭ ਜਗ ਭਯੋ ਜੈ ਜੈ ਜੈ ਸੁਰ ਲੋਕਿ ॥੧੬॥
Whit the world Iamented, the gods hailed his arrival in heavens.16.
Then direct them to famous shabad in Bachitar Natak.
ਅਬ ਮੈ ਅਪਨੀ ਕਥਾ ਬਖਾਨੋ ॥ ਤਪ ਸਾਧਤ ਜਿਹ ਬਿਧਿ ਮੁਹਿ ਆਨੋ ॥
Now I relate my own story as to how I was brought here, while I was absorbed in deep meditation.